[wip] [skip ci] Remove extraneous responsibilities of courier

[lukasolson]

Summary

Part of #34022.

• Simplifies the way search strategies are looked up and assigned
• Removes the search poller and moves the responsibility to the timefilter service
• Removes the search request queue and moves responsibility to fetchSoon
• Search request queue should only contain search requests, not a mix including request statuses
• Removes most of the lifecycle from search request (it wasn't being used)
• Simplifies handling of aborted requests
• Simplifies SearchRequest interface & removes things that were unimplemented (like incomplete/retry/continue)
• Removes logic surrounding querying time-based interval index patterns

Checklist

• This was checked for cross-browser compatibility, including a check against IE11
• 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
• This was checked for keyboard-only and screenreader accessibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately
• This includes a feature addition or change that requires a release note and was labeled appropriately

[lukasolson]

These are filtered as part of the call below in buildEsQuery

[lukasolson]

This logic was over-complicated and moved here

[lukasolson]

Decided to close in favor of #38737.