[Search] Search Playground - shared rendering

[TattdCodeMonkey]

Summary

*** THIS PR IS Extends work done in #200314

This PR removes Search Playground rendering from enterprise_search in favor of search_playground rendering the UI for both Serverless and Stack. Included in this is changes need to support that shift. With this change the search playground UI is now enabled by default, and the search playground plugin explicitly disabled for other Serverless projects.

Additionally this PR introduces a KibanaFeature specifically for searchPlayground so that it can be controlled independently from the entire search feature set.

Checklist

• [x] Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• [ ] Documentation was added for features that require explanation or tutorials
• [ ] Unit or functional tests were updated or added to match the most common scenarios
• [ ] Flaky Test Runner was used on any tests changed
• [ ] The PR description includes the appropriate Release Notes section, and the correct release_note:* label is applied per the guidelines

[elasticmachine]

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[TattdCodeMonkey]

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