- PostgreSQL high availability documentation does not mention
  `max_replication_slots` which must be set to work properly as the
  default value is zero.

Resolves: https://gitlab.com/gitlab-org/gitlab-ce/issues/65700

Related: https://gitlab.com/gitlab-org/omnibus-gitlab/issues/4576

Related: https://gitlab.com/gitlab-org/distribution/team-tasks/issues/438Signed-off-by: Robert Marshall <rmarshall@gitlab.com>