[App Search] Minor const cleanup

[cee-chen]

Summary

Minor cleanup PR. We have some temporary i18n constants hanging out in engine/constants.ts that I've opted to preemptively create folders+constants files for ahead of time. This should make new component folder changes a little less of a headache in the future, + it's less likely we'll forget to update/clean up engine/constants.ts as we go.

Checklist

• Engine nav still working as before and correctly showing titles
• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support

[cee-chen]

NOTE TO SELF: this will have a merge conflict with #87752 (in analytics/index.ts) so either PR needs to be updated depending on which one is merged in first

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: ef261bf

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
enterpriseSearch	1054	1069	+15

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
enterpriseSearch	1.8MB	1.8MB	-200.0B

History

• 💔 Build #98001 failed 127076226e5f49ad1df5de971d327029696cee34
• 💔 Build #97997 failed 72ad74be2f158a81ad80ca09bca50f94d0c2d27b

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@elasticmachine merge upstream