Update PostgreSQL replication settings

What does this merge request do and why?

• Configuration option wal_keep_segments was renamed in PG 13. Currently, setting up GEO in GDK breaks due to this.
• The check for whether or not to use recovery.conf was hardcoded for PostgreSQL 12. It should match everything above 12.

How to set up and validate locally

1. Use the easy installation method to setup Geo. It should fail, and the primary postgresql instance will be refusing to start
2. Use this branch, and the installation should succeed

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.