Make label compatible with existing ones

[Mic92]

Our current labels start with number for priority and also have a color scheme according to priority: NixOS/nixpkgs#92249
Marvin should also follow the same scheme.

[blaggacao]

I'd wait for GA version of marvin, since "looking official" implies stronger stability guarantees.

[timokau]

I don't think it should follow that scheme. There is not much to be gained, and the priority number is a major inconvenience when handling those labels. That is especially true for labels that we want people to actively search for. They would now have to remember/look up the somewhat arbitrary number prefix and probably quote the label in the search. Additionally its nice to have a 1:1 match between the labels and the status names.

(Also, not all current nixpkgs label match that scheme.)

Colors could be added of course, I don't mind that.