Add orphaned Administration topics to the global nav

This MR adds several orphaned topics to the documentation global nav

• https://docs.gitlab.com/ee/administration/package_information/postgresql_versions.html

• https://docs.gitlab.com/ee/administration/pages/source.html

• https://docs.gitlab.com/ee/administration/redis/replication_and_failover.html

• https://docs.gitlab.com/ee/administration/redis/replication_and_failover_external.html

• https://docs.gitlab.com/ee/administration/redis/standalone.html

• https://docs.gitlab.com/ee/administration/redis/troubleshooting.html

• Link to the merge request of the new page:

• Give the MR a descriptive title.

• Link to the merge request that introduced the new page.