[OTHER] add issue assignment GitHub action

[Dun-sin]

What would you like to share?

instead of manually having to assign someone, add the assigned label and remove the up for grabs label, and vise versa when someone is assigned.

We could automate this

Additional information

No response

👀 Have you checked if this issue has been raised before?

• I checked and didn't find similar issue

🏢 Have you read the Contributing Guidelines?

• I have read and understood the rules in the Contributing Guidelines

Are you willing to work on this issue ?

None

[github-actions]

To reduce notifications, issues are locked until they are valid/approved and to be assigned. In the meantime read the contributing guidelines -> https://github.com/Dun-sin/Whisper/blob/main/CONTRIBUTING.md