Allow detection of labels added to PRs

[Greymagic27]

Is there a way to make it so adding a label to a pull request also triggers an action?

Right now I have it setup like that but it only detects labels added to issues and not PRs

[runspired]

basically #97 but for PRs.

These both are a duplicate of #66

I hit this today as well, this bot will move columns based on add/remove label but it won't add PRs as items to the project based on add/remove label. Since there's no rule combo (and no has-label rule) this makes flows based on labels require manually adding the PR to the project, which was a task I was hoping to avoid.