Add database readiness check to registry migrations

What does this MR do?

Add database readiness check to registry migrations

Adds resilience to wait a bit for the PostgreSQL server to be ready before running registry migrations. This is important specially on container registry restarts when the PostgreSQL server lives within the same container.

During container restarts the registry migration is called too early during container startup, since other previous task will be faster than during an usual fresh first time container install, since on fresh installs much more actions are called, like file creations for instance, which will persist on volumes during a container restart and do not need to be redone. Probably many more other things are cached on the volumes and not retriggered on container restart.

Therefore, in these cases, there isn't time enough for PostgreSQL to be up before the registry migration is called. And since the registry migrations are called as part of the main gitlab-ctl reconfigure, if this fails the whole reconfigure fails, which is per Omnibus fail-fast design. This results then in the container being forever restarting.

Solution

Technically this adds the RegistryPgHelper class to override the connection_info method from PgHelper, as in separate nodes we can't use the Rails connection string to do this check. Then we make use of the is_ready? implementation to validate that PostgreSQL server is ready to take connections. This method does a few retries before failing and is also configurable.

Issue: gitlab#571936 Changelog: fixed

Related issues

Closes Docker version GitLab 18.3/18.4 crash when rest... (gitlab#571936)

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