Announcements displayed with wrong admin, should be anonymous

I think I've found a bug, but it's very rare since this software is so awesome :1st_place_medal: :trophy: :clap: :pray:

**Describe the bug**

As an admin of a Mastodon instance, I have posted an announcement to the instance's followers.

However, another admin is shown as the sender of the announcement. This is probably because that admin is the public-facing main contact. I'm just a "co-admin".

On the Mastodon web client, no admins are shown next to announcements, making it possible to send out announcements without a personal sender.

**To Reproduce**

Write an announcement on a server. See that it is displayed with an admin's profile.

**Expected behavior**

Announcements should be anonymous since:

1) An announcement may be added by a specific admin on behalf of an entire group of admins
2) The wrong admin is displayed in some cases.

**Screenshots**


Same announcement in Mastodon:


No file or test is named. Start by reproducing an announcement in the web client and trace the announcement rendering path; compare it with the Mastodon example. Done means announcements display without any admin profile or sender identity.

Written by the indexing model from the issue text.