[8.x] TBS: make storage_limit follow processor lifecycle; update TBS processor config (backport #15488)

[mergify]

Motivation/summary

Fix a regression from #15235 where storage_limit does not follow processor lifecycle.
Remove storage limit from processor config.
Add storage to processor config validation.

Checklist

- [ ] Update CHANGELOG.asciidoc Fixing a regression from an unreleased change

• Documentation has been updated

For functional changes, consider:

• Is it observable through the addition of either logging or metrics?
• Is its use being published in telemetry to enable product improvement?
• Have system tests been added to avoid regression?

How to test these changes

Should be tested along #15235 . Ensure that EA hot reload applies the new storage limit by changing the integration policy.

Related issues

---

This is an automatic backport of pull request #15488 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of dcb08ac has failed:

On branch mergify/bp/8.x/pr-15488
Your branch is up to date with 'origin/8.x'.

You are currently cherry-picking commit dcb08ac9.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	both modified:   x-pack/apm-server/main.go
	both modified:   x-pack/apm-server/sampling/config.go
	both modified:   x-pack/apm-server/sampling/config_test.go
	deleted by us:   x-pack/apm-server/sampling/eventstorage/rw.go
	deleted by us:   x-pack/apm-server/sampling/eventstorage/rw_test.go
	both modified:   x-pack/apm-server/sampling/eventstorage/storage_bench_test.go
	both modified:   x-pack/apm-server/sampling/eventstorage/storage_manager.go
	deleted by us:   x-pack/apm-server/sampling/eventstorage/storage_manager_bench_test.go
	both modified:   x-pack/apm-server/sampling/eventstorage/storage_manager_test.go
	both modified:   x-pack/apm-server/sampling/processor.go
	both modified:   x-pack/apm-server/sampling/processor_test.go

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[mergify]

This pull request has not been merged yet. Could you please review and merge it @carsonip? 🙏

[carsonip]

Closing the PR as we do not intend to bring this back to 8.x due to migration implications.