Ability to sponsor a request

Occasionally, a person who is not a DD makes a request. Sometimes, it's a no brainer for the DPL or approver to approve, but usually in these cases we want a DD to vouch for their request (usually a DD they have worked with or are in their team who can confirm their travel/hardware/etc) is for the benefit of Debian.

Not sure what the best workflow is for this. Perhaps a submitter can enter the login name(s) of a DD who they expect to sponsor their request, then that person would also have access to that ticket so that they could comment, perhaps with some additional checkbox to say "I endorse this request". Although I don't care too much about the specific implementation so I'll leave that up to you.