Refactor PG Upgrade

What does this merge request do and why?

This is a refactor of PostgresUpgrader to reduce the surface area and allow a future extraction/generalization to support Geo PostgreSQL installations

This initial refactor focus on extracting most of the utilitarian logic that is not specific to the Upgrade process

In a future MR the Upgrader class will be made more generic to support pointing to a different installation location in order to support both the regular PostgreSQL as well as the Geo Tracking Database.

How to set up and validate locally

This is just a refactor, it doesn't include any behaviour change. The upgrader should still work as it did before

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.