Tidy up the dependency proxy docs

What does this merge request do and why?

This is a docs-only update for the dependency proxy page.

It does the following:

1. Removes the mention about the license requirements since the dependency proxy is now a core feature.
2. Adds information on how to configure an insecure registry for Colima (which is commonly used in Engineering as a Docker replacement, see the handbook here)
3. Adds the docker login command
4. Restructures the Docker daemon section

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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.