Increase the number of DB maintainers

As of today there is only 1 DB reviewer and maintainer at GitLab (who is doing outstanding work). With the increasing number of engineering contributing to the product we need to work to add additional reviewers and maintainers in this area.

This issue is created based on a topic that was raised during the 12.0 retrospective and where we can discuss options as well as a plan to address this issue.

cc @DylanGriffith @abrandl @stanhu @clefelhocz1 @timzallmann @cdu1 @bmarnane @tstadelhofer for awareness

We currently have 8 individuals as database trainee_maintainers - https://gitlab.com/gitlab-com/www-gitlab-com/issues?scope=all&utf8=%E2%9C%93&state=all&label_name[]=trainee%20maintainer&search=database

Three of these are listed as database reviewers in the handbook - https://about.gitlab.com/handbook/engineering/projects/#gitlab-ce_maintainers_database

Follow up Actions:

• Update Trainee database maintainer.md to include step to move from reviewer database to trainee_maintainer database - gitlab-com/www-gitlab-com!27278 (diffs)
• Request current reviewers change to trainee_maintainer database in team.yml
• Add note to Engineering Week In Review asking for more team members to join as trainee_maintainer
• Add entry in Company Call asking for more team members to join as trainee_maintainer