Mention limitations of MySQL in docs
What does this MR do?
Document the limitations of MySQL and why users should switch using PostgreSQL instead.
Mostly ticks the checkboxes in https://gitlab.com/gitlab-org/gitlab-ce/issues/30472#note_29072566
Document the limitations of MySQL and why users should switch using PostgreSQL instead.
Mostly ticks the checkboxes in https://gitlab.com/gitlab-org/gitlab-ce/issues/30472#note_29072566