Suggest alternatives if an invalid command is supplied

What does this Merge Request do and why?

Uses did_you_mean to suggest possible alternatives to invalid GDK commands (ie typos).

Before:

$ gdk rstart
⚠️  WARNING: gdk rstart is not a GDK command.
ℹ️  See 'gdk help' for more detail.

After:

$ gdk rstart
⚠️  WARNING: rstart is not a GDK command.
⚠️  WARNING: Did you mean?  restart
⚠️  WARNING:                start

ℹ️  See 'gdk help' for more detail.

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.