Add option to unassign an issue

[mowies]

Description: I would like to propose an option to unassign an issue when it becomes stale.

Justification: My use case: In https://github.com/keptn/lifecycle-toolkit, we have a list of good-first-issues but it happens, that contributors stop working on things or don't reply anymore for whatever reason. I want to use this action to add a call to action to those "inactive" issues telling the contributors to give an update on the status and then if no further activity is seen in the ticket, unassign it so that other contributors can work on it.

Are you willing to submit a PR? yes

[dsame]

Hello @mowies , thanks for your suggestion. We will start investigate the possibility to implement this feature

[dfawley]

+1 - especially with Hacktoberfest going on right now, we've had several people try to claim issues, but then disappear. Being able to automatically unassign them after a week or two would be a great feature.