Draft: Add on and off options to draft quick command

What does this MR do and why?

Adds the option to specify an optional on or off to the Merge Request /draft quick action

This allows use in ways where an idempotent version would be useful.

Screenshots or screen recordings

How to set up and validate locally

On a merge request (new or open) you can use the quick action /draft on or /draft off to 'flip the switch' in a specific direction, in addition to /draft to toggle the existing status.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.