As a PR-ansvarig, I want an option to publish to slack, so that I can chose not to have the news blasted the the entire division

### 📝 Description

Sometimes you do not want your newsn posted in slack, for exemple when you want to test out something, so not everybody in the entire division gets a notification about it. Therefore it would be nice to have an option to post on slack or not.

(Also, great work everybody who has been involved in building the new chalmers.it <3 )

### ✅ Acceptance Criteria

- [ ] There is a option to publish a news post to slack
- [ ] The option is selected by default

### 💡 Additional context

_No response_