feat: Useragent handler for announcements

[oSumAtrIX]

Issue

Currently, every announcement consumer receives announcements. This is impractical, considering we may want to make announcements for specific users.

Solution

Add a handler for the user agent. Based on the user agent, the announcement will be supplied or not.

[alexandreteles]

Can you explain it a little better? What architecture do you have in mind?

[oSumAtrIX]

The implementation itself is not in focus. The idea is that we can send announcements based on the user agent. This would allow us to show announcements to specific groups of clients. Maybe this can be specified when creating a new announcement?