[chore] Update kibana/.github/CODEOWNERS to accurately reflect AppArch team areas

[alexh97]

CODEOWNERS setup doesn't accurately reflect Application Architecture team's areas of responsibility. This results in PRs not being automatically assigned to the team for review. The current practice is for developers to manually add the team as a reviewer.

We should update the CODEOWNERS setup to reflect the directories that should fall under App Arch area of responsibility.

[elasticmachine]

Pinging @elastic/kibana-app-arch

[streamich]

Was actually adding some of our folders in this PR: https://github.com/elastic/kibana/pull/47810/files#diff-5cfb934ca0ec4c1743905a51dc428b84R11-R17

[lukeelmers]

I added #51502 to include some not-yet-migrated legacy plugins so that we can close this issue.

At this point we should have a list of plugins that is comprehensive (AFAIK)