Deprecate gdk trust

What does this Merge Request do and why?

⚠ This MR needs !1880 (merged).

This MR deprecates the need to run gdk trust which will result in ${HOME}/.gdk.yml not needing to be written or read. gdk trust never really offered any security benefits.

When this MR is merged and the new gem is available, running gdk trust yields:

$ gdk trust .
ℹ️  'gdk trust' is deprecated and no longer required.

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 Issue to follow-up.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.