[CI] Add check for possible new FTR configs

[brianseeders]

This check will catch most (but not all) new FTR configs that are added to the repo without being added to .buildkite/ftr_configs.yml. Several users have added new configs without adding them there, and I've done it a few times myself.

As of writing, when run against every file in the repo, it identifies about 90% of FTR configs with 0 false positives.

Also, the precommit hook is currently broken, because combineErrors was moved out of @kbn/dev-utils, so this fixes that as well.

[elasticmachine]

Pinging @elastic/kibana-operations (Team:Operations)

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: fe531c0
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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
@kbn/test	201	202	+1

Unknown metric groups

API count

id	before	after	diff
@kbn/test	240	241	+1

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

[jbudz]

Is it worth adding a CI check for this? LGTM as a standalone change too.

[brianseeders]

Is it worth adding a CI check for this? LGTM as a standalone change too.

I've gone back and forth about adding a check against all files in the repo. I'm not sure if I want it to always run like that, especially since the check isn't 100% accurate.

The precommit hook checks do run as part of CI