[Fleet] Add cache-control headers to key /epm endpoints in Fleet API

[kpollich]

Summary

Resolves #125794

Improve performance throughout the Integrations UI by caching key responses around integrations data:

• GET /api/fleet/epm/categories - "Browse integrations" grid side panel
• GET /api/fleet/epm/packages - "Browse integrations" grid data
  • Also supports an optional excludeInstallStatus parameter that allows us to opt-in to caching on the "Browse integrations" tab when we can afford to cache package list data
• GET /api/fleet/epm/packages/<name>/<version>/<file path> - Allows for caching requests for assets like README.md files, etc

Each of these endpoints has a cache-control header w/ value max-age: 600 added, so they'll be cached for 10 minutes. Further improvements could be made in the future around more granular caching values for each endpoint, or investigating the usage of the stale-while-revalidate cache directive to avoid heavy un-cached requests once the cache is stale.

I've included some network tab screenshots and notes around each of these requests below:

View screenshots

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[juliaElastic]

LGTM

[kpollich]

@elasticmachine merge upstream

[kpollich]

I'm going to swap the includeInstallStatus query string for an excludeInstallStatus query string because I think we have more cases where we want the install status included than we want it excluded.

[joshdover]

I'm going to swap the includeInstallStatus query string for an excludeInstallStatus query string because I think we have more cases where we want the install status included than we want it excluded.

Makes sense to me. I think this would be a breaking change otherwise too, no?

[kibana-ci]

💚 Build Succeeded

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Metrics [docs]

Public APIs missing comments

Total count of every public API that lacks a comment. Target amount is 0. Run node scripts/build_api_docs --plugin [yourplugin] --stats comments for more detailed information.

id	before	after	diff
fleet	1267	1268	+1

Async chunks

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

id	before	after	diff
fleet	693.3KB	693.4KB	+24.0B

Unknown metric groups

API count

id	before	after	diff
fleet	1384	1385	+1

History

• 💔 Build #40516 failed 6dff748
• 💔 Build #40356 failed 8adb646
• 💔 Build #40328 failed d5510bf

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @kpollich

[criamico]

LGTM

[kpollich]

I'm going to swap the includeInstallStatus query string for an excludeInstallStatus query string because I think we have more cases where we want the install status included than we want it excluded.

Makes sense to me. I think this would be a breaking change otherwise too, no?

Yep you are correct. Latest commit here has this change implemented and all is green, so I'm landing this.