Add Geo rake task for checking tracking DB after promotion

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What does this MR do and why?

This MR resolves #421340 (closed) by adding a new Geo rake check task (rake gitlab:geo:check). It checks if a Geo primary contains old secondary-related config entries, which should not be the case after a promotion.

TODOs:

• Rubocop offense?

  ee/lib/system_check/geo/geo_database_promoted_check.rb:3:8: C: Gitlab/BoundedContexts: Module SystemCheck is not a valid bounded context.
  See https://docs.gitlab.com/ee/development/software_design#bounded-contexts.
  module SystemCheck
         ^^^^^^^^^^^

• Spec tests?
  • If secondary, skip
  • If primary, no tracking DB
  • If primary, with tracking DB
• User docs?
  • The rake task is already being mentioned on various pages
• Changelog?

🔧 with at Adfinis

References

• #421340 (closed)

Screenshots or screen recordings

How to set up and validate locally

1. Deploy a Geo primary and secondary
2. Run check against primary, it should pass
3. Run check against secondary, it should be skipped
4. Add secondary config to primary, it should fail

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