On our dev instance, /admin/applications as not loading because:
1. There was an unindexed query by `application_id`.
2. There was an expensive query that attempted to load 1 million
unique entries via ActiveRecord just to find the unique count.
We fix the first issue by adding an index for that column.
We fix the second issue with a simple SELECT COUNT(DISTINCT
resource_owner_id) SQL query.
In addition, we add pagination to avoid loading more than 20
applications at once.
Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/67228
In 8278b763d9 the default behaviour of annotation
has changes, which was causing a lot of noise in diffs. We decided in #17382
that it is better to get rid of the whole annotate gem, and instead let people
look at schema.rb for the columns in a table.
Fixes: #17382
