GitHub action to validate is any user is assigned to pull request

[adamfilipow92]

Author the user story for this feature

As a pull request author, I want to be informed when I forgot to assign my self to pull request so I can avoid empty author on release notes.

Is your feature request related to a problem? Please describe.

I forgot to assign myself to this pr: https://github.com/Flank/flank/pull/1087this cause no author assigned in release notes,

- [#1087](https://github.com/Flank/flank/pull/1087) Fix release action ()

#1089

Describe the solution you'd like
Action should fail when no one is assigned to pull requests.

Describe alternatives you've considered

The alternative is assign the author of the first commit in pull request.

[Sloox]

@adamfilipow92 I saw this github action. It might not check exactly but it can be triggered first and will do all the work automatically.
https://github.com/marketplace/actions/auto-assign-action

[bootstraponline]

Maybe we should create a github action that copies the label, estimation, and asignees from the issue referenced in the pull request to the pull request itself. This would involve using the ZenHub API.

• https://github.com/ZenHubIO/API