[SIEM][Detection Engine] Adds the default name space to the end of th…

…e signals index

## Summary

One liner to add the `default` to the end of the siem signals index for people to play with it.

### 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~~

~~- [ ] [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)~~

~~- [ ] 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/public/pages/detection_engine/signals/index.tsx

@@ -64,7 +64,7 @@ export const SignalsTable = React.memo(() => {
       <GlobalTime>
         {({ to, from, setQuery, deleteQuery, isInitializing }) => (
           <StatefulEventsViewer
-            defaultIndices={[DEFAULT_SIGNALS_INDEX]}
+            defaultIndices={[`${DEFAULT_SIGNALS_INDEX}-default`]}
             defaultFilters={filterGroup === FILTER_OPEN ? signalsOpenFilters : signalsClosedFilters}
             defaultModel={signalsDefaultModel}
             end={to}