Add announcements block to the welcome dashboard

Needs review.

Looks fine to me from a code perspective.

...but I'm gonna seek final sign-off from Pam.

@penyaskito convinced me in Slack that this is already pre-approved by Pam. Although I'd certainly appreciate her manually testing it, I think the risk here is low enough that it's worth merging now in the name of keeping the track moving quickly.

Merged into 0.x.

Created 📌 Announcements date format in Drupal CMS Dashboard Active as follow-up

Thanks gents, agree that approval was implicit in the designs!

Automatically closed - issue fixed for 2 weeks with no activity.