Enable Geo Tracking Database

The next step to enabling Geo for GitLab.com is to enable the tracking database. This is not as straightforward as the documentation suggests, so I am creating this issue to track.

The replicated main databases are set up. There is a separate instance configured for the tracking database at the secondary site. We are at the point of running the migrations to set up the schema.

This issue can be closed when this section of the documentation is successfully completed: https://docs.gitlab.com/ee/administration/geo/replication/external_database.html#configure-the-tracking-database

cc/ @ashmckenzie