feat: add banner for new bulletin

[fotisolgr]

Hey it would be nice for backstage users to receive mails every time a new bulletin card is created or every time a card is created with a specific tag. WDYT?

[v-ngu]

Do you have any suggestions on how to do it as probably not everyone would want notifications?

[markandersontrocme]

I would suggest something similar to the Announcements plugin where you can add a Banner for new announcements.

This allows it to be flexible in that Banners can enabled/disabled for each implementation.

[fotisolgr]

Totally agree with @markandersontrocme. I'm already using Announcements plugin and this feature is quite comfy imo.