[Getting Started] Deprecate feature flag (part 2 of 2)

[wildemat]

Closes 11480

Summary

This PR depends on [Getting Started] Deprecate feature flag (part 1 of 2)

• Remove all usage of the searchSolution.gettingStartedEnabled feature flag from application and test code
• search_getting_started solution FTRs are moved into the main config.ts runner
• Hosted nav tests were updated to expect getting started plugin

[elasticmachine]

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