repmgr gitlab-ctl command has hardcoded data locations

The repmgr gitlab-ctl command has a few hard-coded data and config file locations that cause problems if customers have moved data locations. All paths should use configured values from /etc/gitlab/gitlab.rb.

In lib/repmgr.rb:

• PostgreSQL data directory - cmd("rm -rf /var/opt/gitlab/postgresql/data")
• repmgr.conf file path - cmd("/opt/gitlab/embedded/bin/repmgr #{args[:verbose]} -f /var/opt/gitlab/postgresql/repmgr.conf #{command}", runas)