Manual control of issue states

[birkjernstrom]

Ability for maintainer to manually move issues between our different states.

E.g might start working on something before a draft PR / commit is even published and would be nice to signal that to backers. Or moving it to triaged even if it doesn't meet the automatic triaged states etc. In short: Allowing maintainers to keep their backers informed beyond the automatic updates.

[birkjernstrom]

Including explicitly confirming a pledged issue as completed once it's closed

[birkjernstrom]

Moved into issues as an epic: #663