Add MR mergeability check for locked paths

This change introduces a new check. This check will prevent merging MRs
which include locked paths.

We also have a check which runs when a user pushes code that prevents
pushing paths that are locked by other users.

This change will allow us to enable the fix for
https://gitlab.com/gitlab-org/gitlab/-/issues/23625

Related to https://gitlab.com/gitlab-org/gitlab/-/issues/428247

Changelog: added

# Conflicts:
#	app/assets/javascripts/vue_merge_request_widget/components/checks/constants.js
#	app/graphql/types/merge_requests/detailed_merge_status_enum.rb
#	app/models/merge_request.rb
#	doc/api/graphql/reference/index.md
#	doc/api/merge_requests.md
#	ee/app/models/ee/merge_request.rb