Merge branch 'sy-combine-metrics-schema' into 'master'

Combine json-schemas for metrics into a single file

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/143432



Merged-by: Jarka Košanová <jarka@gitlab.com>
Approved-by: Piotr Skorupa <pskorupa@gitlab.com>
Approved-by: Jarka Košanová <jarka@gitlab.com>
Co-authored-by: Sarah Yasonik <syasonik@gitlab.com>