Block non-signed commits per-repo or per-instance

[benyanke]

Feature request: my team has begun using signed commits for some projects. It would be useful to have a checkbox in the repo to reject non-signed commits to enforce this server side, perhaps with a less strict (only users with a key in their profile have this checked) and more strict mode (any commit must be signed).

[jolheiser]

Do you mean #9708? That PR should be included in 1.12.x

[benyanke]

Yup, that's basically what I had in mind.

Good work as always!