#380 Add announcement options

Hello there, this is to be a meta-discussion about how we might add announcement options to inform the Codeberg community about cool things 👋 Directly related: the discussion about a 💵 funding campaign in #337, but also discussions about changes in the ToS (e.g. to delete inactive users/repos) etc where users should probably be informed as well. And there are likely other things we want to announce, like community polls, updates to the software etc ... Let's consider whether we want an announcement banner (e.g. at the top of the dashboard), or more like a notification inside the notification system ... whether it should be dismissable ... and how to achieve this. Thank you 🚀