Merge branch 'ph/mergeRequestDashboardLoading' into 'master'

Added loading indicator to each section on the merge request dashboard

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/151678



Merged-by: Jose Ivan Vargas <jvargas@gitlab.com>
Approved-by: Jose Ivan Vargas <jvargas@gitlab.com>
Reviewed-by: Jose Ivan Vargas <jvargas@gitlab.com>
Co-authored-by: Phil Hughes <me@iamphill.com>