Add a reconfigure step after initializing data dir or downgrading PostgreSQL

What does this Merge Request do?

After downgrading PostgreSQL or initializing a new data directory, we need to run gdk reconfigure.

Merge Request checklist

• Tests added for new functionality. If not, please raise Issue to follow-up.
• This change is backward compatible. If not, please include steps to communicate to our users.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.