During upgrade, detect if an external PostgreSQL database is used and provide correct docs link
When upgrading GitLab with an external database (
yum update), GitLab provides messaging about newer versions of PostgreSQL being available. For example,
GitLab now ships with a newer version of PostgreSQL (11.7). To upgrade, please see: https://docs.gitlab.com/omnibus/settings/database.html#upgrade-packaged-postgresql-server. This link is provided, even if the user is using an external PostgreSQL database rather than the packaged database.
GitLab should be able to detect if an external database is being used based on
postgresql['enable'] = false and connection details are set. If an external database is detected, upgrade messages should point to a section in https://docs.gitlab.com/omnibus/settings/database.html that is specifically for updating external databases. This section still needs to be created.