[SIEM][Detection Engine] Fixes critical regression on the backend wit…

…h immutable and tags

## Summary

Fixes regression with immutable caused from:
#55004

* Updated types of Prepackaged 
* Updated unit tests
* Fixed unit test for it

Testing:

```
./post_rule.sh 
{
  "created_at": "2020-01-17T19:11:31.813Z",
  "updated_at": "2020-01-17T19:11:31.813Z",
  "created_by": "elastic_kibana",
  "description": "Query with a rule_id that acts like an external id",
  "enabled": true,
  "false_positives": [],
  "from": "now-6m",
  "id": "41ef6309-ef98-4c9f-8d2d-90a070361fb7",
  "immutable": false,
  "interval": "5m",
  "rule_id": "query-rule-id",
  "language": "kuery",
  "output_index": ".siem-signals-frank-hassanabad-default",
  "max_signals": 100,
  "risk_score": 1,
  "name": "Query with a rule id",
  "query": "user.name: root or user.name: admin",
  "references": [],
  "severity": "high",
  "updated_by": "elastic_kibana",
  "tags": [],
  "to": "now",
  "type": "query",
  "threats": [],
  "version": 1
}
```

Then get the saved object using whatever the id is comes back from above. In this example it is 41ef6309-ef98-4c9f-8d2d-90a070361fb7, yours will be different

```
./get_saved_objects.sh alert 41ef6309-ef98-4c9f-8d2d-90a070361fb7
{
  "id": "41ef6309-ef98-4c9f-8d2d-90a070361fb7",
  "type": "alert",
  "updated_at": "2020-01-17T19:11:32.844Z",
  "version": "WzY5NTQsMV0=",
  "attributes": {
    "name": "Query with a rule id",
    "tags": [
      "__internal_rule_id:query-rule-id",
      "__internal_immutable:false"
    ],
    "alertTypeId": "siem.signals",
    "consumer": "siem",
    "params": {
      "createdAt": "2020-01-17T19:11:31.813Z",
      "description": "Query with a rule_id that acts like an external id",
      "ruleId": "query-rule-id",
      "index": null,
      "falsePositives": [],
      "from": "now-6m",
      "immutable": false,
      "query": "user.name: root or user.name: admin",
      "language": "kuery",
      "outputIndex": ".siem-signals-frank-hassanabad-default",
      "savedId": null,
      "timelineId": null,
      "timelineTitle": null,
      "meta": null,
      "filters": null,
      "maxSignals": 100,
      "riskScore": 1,
      "severity": "high",
      "threats": [],
      "to": "now",
      "type": "query",
      "updatedAt": "2020-01-17T19:11:31.813Z",
      "references": [],
      "version": 1
    },
    "schedule": {
      "interval": "5m"
    },
    "enabled": true,
    "actions": [],
    "throttle": null,
    "apiKeyOwner": "elastic_kibana",
    "createdBy": "elastic_kibana",
    "updatedBy": "elastic_kibana",
    "createdAt": "2020-01-17T19:11:32.245Z",
    "muteAll": false,
    "mutedInstanceIds": [],
    "scheduledTaskId": "2c5cc340-395d-11ea-9276-d3c1c264ca9a"
  },
  "references": []
}
```

Ensure you have the internal immutable of "__internal_immutable:false" In your tags


Next test is to do a find filter of non-packaged rules:

```
./find_rule_by_filter.sh "alert.attributes.tags:%20%22__internal_immutable:false%22"
```

You should get back the above rule any others you created.

### Checklist

Use ~~strikethroughs~~ to remove checklist items you don't feel are applicable to this PR.

~~- [ ] This was checked for cross-browser compatibility, [including a check against IE11](https://github.com/elastic/kibana/blob/master/CONTRIBUTING.md#cross-browser-compatibility)~~

~~- [ ] Any text added follows [EUI's writing guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses sentence case text and includes [i18n support](https://github.com/elastic/kibana/blob/master/packages/kbn-i18n/README.md)~~

~~- [ ] [Documentation](https://github.com/elastic/kibana/blob/master/CONTRIBUTING.md#writing-documentation) was added for features that require explanation or tutorials~~

- [x] [Unit or functional tests](https://github.com/elastic/kibana/blob/master/CONTRIBUTING.md#cross-browser-compatibility) were updated or added to match the most common scenarios

~~- [ ] This was checked for [keyboard-only and screenreader accessibility](https://developer.mozilla.org/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Accessibility#Accessibility_testing_checklist)~~

### For maintainers

~~- [ ] This was checked for breaking API changes and was [labeled appropriately](https://github.com/elastic/kibana/blob/master/CONTRIBUTING.md#release-notes-process)~~

- [x] This includes a feature addition or change that requires a release note and was [labeled appropriately](https://github.com/elastic/kibana/blob/master/CONTRIBUTING.md#release-notes-process)

x-pack/legacy/plugins/siem/server/lib/detection_engine/routes/__mocks__/request_responses.ts

@@ -18,9 +18,9 @@ import {
   DETECTION_ENGINE_PREPACKAGED_URL,
 } from '../../../../../common/constants';
 import { RuleAlertType, IRuleSavedAttributesSavedObjectAttributes } from '../../rules/types';
-import { RuleAlertParamsRest } from '../../types';
+import { RuleAlertParamsRest, PrepackagedRules } from '../../types';
 
-export const fullRuleAlertParamsRest = (): RuleAlertParamsRest => ({
+export const mockPrepackagedRule = (): PrepackagedRules => ({
   rule_id: 'rule-1',
   description: 'Detecting root and admin users',
   index: ['auditbeat-*', 'filebeat-*', 'packetbeat-*', 'winlogbeat-*'],
@@ -51,8 +51,6 @@ export const fullRuleAlertParamsRest = (): RuleAlertParamsRest => ({
   false_positives: [],
   saved_id: 'some-id',
   max_signals: 100,
-  created_at: '2019-12-13T16:40:33.400Z',
-  updated_at: '2019-12-13T16:40:33.400Z',
   timeline_id: 'timeline-id',
   timeline_title: 'timeline-title',
 });

x-pack/legacy/plugins/siem/server/lib/detection_engine/routes/rules/create_rules_bulk_route.ts

@@ -55,7 +55,6 @@ export const createCreateRulesBulkRoute = (server: ServerFacade): Hapi.ServerRou
             enabled,
             false_positives: falsePositives,
             from,
-            immutable,
             query,
             language,
             output_index: outputIndex,
@@ -109,7 +108,7 @@ export const createCreateRulesBulkRoute = (server: ServerFacade): Hapi.ServerRou
               enabled,
               falsePositives,
               from,
-              immutable,
+              immutable: false,
               query,
               language,
               outputIndex: finalIndex,

x-pack/legacy/plugins/siem/server/lib/detection_engine/routes/rules/create_rules_route.ts

@@ -39,7 +39,6 @@ export const createCreateRulesRoute = (server: ServerFacade): Hapi.ServerRoute =
         enabled,
         false_positives: falsePositives,
         from,
-        immutable,
         query,
         language,
         output_index: outputIndex,
@@ -96,7 +95,7 @@ export const createCreateRulesRoute = (server: ServerFacade): Hapi.ServerRoute =
           enabled,
           falsePositives,
           from,
-          immutable,
+          immutable: false,
           query,
           language,
           outputIndex: finalIndex,

x-pack/legacy/plugins/siem/server/lib/detection_engine/routes/rules/update_rules_bulk_route.ts

@@ -44,7 +44,6 @@ export const createUpdateRulesBulkRoute = (server: ServerFacade): Hapi.ServerRou
             enabled,
             false_positives: falsePositives,
             from,
-            immutable,
             query,
             language,
             output_index: outputIndex,
@@ -77,7 +76,6 @@ export const createUpdateRulesBulkRoute = (server: ServerFacade): Hapi.ServerRou
               enabled,
               falsePositives,
               from,
-              immutable,
               query,
               language,
               outputIndex,

x-pack/legacy/plugins/siem/server/lib/detection_engine/routes/rules/update_rules_route.ts

@@ -33,7 +33,6 @@ export const createUpdateRulesRoute: Hapi.ServerRoute = {
       enabled,
       false_positives: falsePositives,
       from,
-      immutable,
       query,
       language,
       output_index: outputIndex,
@@ -75,7 +74,6 @@ export const createUpdateRulesRoute: Hapi.ServerRoute = {
         enabled,
         falsePositives,
         from,
-        immutable,
         query,
         language,
         outputIndex,