Update documentation for the PostgreSQL 9.6 and 10 removals
PostgreSQL 9.6 and 10 are being removed in GitLab 13.0. We should remove any documentation for these two versions of PostgreSQL and add a note that they are no longer supported.
PostgreSQL 9.6 and 10 are being removed in GitLab 13.0. We should remove any documentation for these two versions of PostgreSQL and add a note that they are no longer supported.