dependencies: Use psql from postgresql.bin_dir

What does this merge request do and why?

The user can configure postgresql.bin_dir in their gdk.yml. This bypasses the scripts to auto-detect the location of psql. And in 52599d0a (support: Use pg_config from gdk config, 2023-06-08) we modified the bootstrap scripts to properly use psql from postgresql.bin_dir.

To check the dependencies, this bin_dir also should be used, instead of searching for a possible location ourselves.

How to set up and validate locally

1. Set a path for postgresql.bin_dir in your gdk.yml.
2. Run rake preflight-checks.

Depending on the existence of psql in the given postgresql.bin_dir, or the version used, the preflight-checks should PASS/FAIL.

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.