Add a CODEOWNERS file

What does this MR do?

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

.gitlab/CODEOWNERS

+# Backend Maintainers are the default for all ruby files
+*.rb @ayufan @DouweM @dzaporozhets @grzesiek @nick.thomas @rspeicher @rymai @smcgivern
+*.rake @ayufan @DouweM @dzaporozhets @grzesiek @nick.thomas @rspeicher @rymai @smcgivern
+
+# Technical writing team are the default reviewers for everything in `doc/`
+/doc/ @axil @marcia
+
+# Frontend maintainers should see everything in `app/assets/`
+app/assets/ @annabeldunstone @ClemMakesApps @fatihacet @filipa @iamphill @mikegreiling @timzallmann
+
+# Someone from the database team should review changes in `db/`
+db/ @abrandl @NikolayS
+
+# Feature specific owners
+/ee/lib/gitlab/code_owners/ @reprazent

[QA User (Quality Team's Test Account)]

hey what sup

[Douwe Maan]

Test!

[QA User (Quality Team's Test Account)]

and howz it going??

[Douwe Maan]

Test!

[Douwe Maan]

Test