Support running manually #3

It would be cool if the action didn't rely only on issue or pull_request events, but could also be run manually.

You could have previous steps changing the labels but not triggering an action run, so it would be useful to trigger it by providing the issue/PR number as an input

This would also open the possibility of using workflow_dispatch, or other event types.

This would also mean that we could add a way to run it with multiple issue/pr numbers.