Add Maintenance Titles and Descriptions

**Is your feature request related to a problem? Please describe.**
It‘s just very unclear to visitors why systems are under maintenance.

**Describe the solution you'd like**
It would be cool to have optional maintenance titles and descriptions where you could tell users what you are doing with your systems. If a description was set for one/multiple service/s, a box should show up below the status bar on a public status page that should show the Maintenance Title, description, affected services and estimated end of the maintenance window in their timezone / remaining Days/Hours/Minutes(/Seconds).

**Additional context**
Such a box could look like this (prototype):
**Title**
Affected Systems: \ (<- small text)
———————————————
Description
———————————————
Maintenance concludes at \ | in \

I have more ideas regarding maintenances but I will split them into multiple issues

Start by reviewing the public status page and the existing maintenance workflow. Define how maintenance titles, descriptions, affected services, end times, and timezone-aware countdowns should be configured and displayed. Done means the proposed behavior and scope are agreed before implementation.

Written by the indexing model from the issue text.