[Fleet] Add support for constant_keyword "value" in package field def…

…initions (elastic#103000)

This enables Fleet to accept package field definitions that declare a constant "value"
for `constant_keyword` fields. Fleet will generate an index template for the constant_keyword
field that contains the `value` attribute.

Relates: elastic/package-spec#194

Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>

x-pack/plugins/fleet/server/services/epm/elasticsearch/template/template.test.ts

@@ -613,6 +613,26 @@ describe('EPM template', () => {
     expect(JSON.stringify(mappings)).toEqual(JSON.stringify(constantKeywordMapping));
   });
 
+  it('tests constant_keyword field type with value', () => {
+    const constantKeywordLiteralYaml = `
+- name: constantKeyword
+  type: constant_keyword
+  value: always_the_same
+  `;
+    const constantKeywordMapping = {
+      properties: {
+        constantKeyword: {
+          type: 'constant_keyword',
+          value: 'always_the_same',
+        },
+      },
+    };
+    const fields: Field[] = safeLoad(constantKeywordLiteralYaml);
+    const processedFields = processFields(fields);
+    const mappings = generateMappings(processedFields);
+    expect(JSON.stringify(mappings)).toEqual(JSON.stringify(constantKeywordMapping));
+  });
+
   it('processes meta fields', () => {
     const metaFieldLiteralYaml = `
 - name: fieldWithMetas

x-pack/plugins/fleet/server/services/epm/elasticsearch/template/template.ts

@@ -150,6 +150,12 @@ export function generateMappings(fields: Field[]): IndexTemplateMappings {
             fieldProps.fields = generateMultiFields(field.multi_fields);
           }
           break;
+        case 'constant_keyword':
+          fieldProps.type = field.type;
+          if (field.value) {
+            fieldProps.value = field.value;
+          }
+          break;
         case 'object':
           fieldProps = { ...fieldProps, ...generateDynamicAndEnabled(field), type: 'object' };
           break;

x-pack/plugins/fleet/server/services/epm/fields/field.ts

@@ -15,6 +15,7 @@ export interface Field {
   name: string;
   type?: string;
   description?: string;
+  value?: string;
   format?: string;
   fields?: Fields;
   enabled?: boolean;

x-pack/plugins/fleet/server/services/epm/fields/tests/base.yml

@@ -20,4 +20,7 @@
   object_type: integer
 - name: invalidarray
   type: array
+- name: cycle_type
+  type: constant_keyword
+  value: bicycle