Expand birdseye configuration options to include 'timeshare' by position

**Describe what you are trying to accomplish and why in non technical terms**
I want to be able to more specifically configure the birdseye view, so that I can designate which square in the matrix should display which cameras and when.

I use one of my Frigate instances to monitor my five 3d printers. Currently I use birdseye motion mode to accomplish this - any printers that are printing show up in the birdseye. However it becomes an issue when all five printers are printing. The birdseye view switches to the 3x2 matrix making it difficult to see the feed of all five printers.

What I'd like to do is have 3 of my cameras set to 'continuous' mode, to keep the 2x2 matrix active at all times. And then for the 4th position, enable a 'timeshare' mode between my two least-used printers. Basically, if set to timeshare mode, it would cycle between the two cameras every, say, 10 seconds.

**Describe the solution you'd like**
Add a 'timeshare' birdseye mode which would cycle thru each camera on that mode based on time.

**Describe alternatives you've considered**
There is a Windows program called RTSP Camera View which can do something similar to what I am describing (not a timeshare, but allows sub-division of matrix spots) but I am unaware of a linux alternative. I still would be using Frigate in the background for recording so I'd rather not have to use an additional app.

**Additional context**
None

The issue names no files, tests, or entry points. Start by locating the birdseye configuration and view implementation, then trace how camera positions and display modes are selected. Done means a configuration can assign a timeshare position and rotate its cameras on the requested interval without changing other positions.

Written by the indexing model from the issue text.