Allow to trigger the site status alert (red button) remotely

Description of the need

We recently did a minor update to 1.19.0 which broke Backup Migrate module. We were worried that there would be a high chance that users would be upgrading their sites before they upgrade BaM, at which point it would crash the site. There were discussions then about how to warn users who were planning to upgrade core that they should upgrade BaM first. That is difficult, as not everyone reads release notes or checks Twitter, or GH, or etc.

Someone proposed a dashboard announcement, but that may not be noticed before upgrading either

Proposed solution

Idea then: what if we chose to allow some announcements to trigger the alert as well? User sees red dot, checks why and sees: "new update available, but recommended upgrade BaM first" or such.

Use judiciously. Make it dismissable.