[Feature]: expanded announcement settings

[tbcsec]

Before you start

• I searched existing issues and this isn't already requested.

What problem does this solve?

Announcements currently only limited to sending out to all teams, and with the same formatting

Proposed solution

Propose implementing the ability to send to a selection of users/teams, as well as different announcement types (informational, warning, danger, etc.) for various levels of urgency, with the most urgent overriding notification individual notification settings.

Alternatives considered

No response

Rough size

Medium (a new screen / endpoint)

Contribution

• I'd be willing to help implement this.