Database goals for July 12th

@yorickpeterse:

• Continue working on the code necessary to query both events and push events as if the data came from a single table: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/12463
• Look into https://gitlab.com/gitlab-org/gitlab-ce/issues/27165 to see what we can do about the SQL timings: https://gitlab.com/gitlab-org/gitlab-ce/issues/27165#note_34811465

Last week's goals can be found at https://gitlab.com/gitlab-com/infrastructure/issues/2136