Merge branch 'db-review-docs-use-actual-query' into 'master'

Add database_reviews docs section describing final query plans

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/130487



Merged-by: Amy Qualls <aqualls@gitlab.com>
Approved-by: Amy Qualls <aqualls@gitlab.com>
Approved-by: Diogo Frazão <dfrazao@gitlab.com>
Co-authored-by: Dylan Griffith <dyl.griffith@gmail.com>