MQTT: Birdseye enabled/disabled and mode change support

[sberryman]

Added two new MQTT topics for adjusting the enabled/disabled state per camera as well as the mode.

This is in draft as there are a few things I'm not a big fan of. This is most likely due to my lack of python experience.

1. BirdseyeModeEnum is a string and camera metrics are using multiprocessing ctypes to sync data between processes. I hacked in an integer based index for support. You probably have a better idea of how this should be done.
2. When testing this out I noticed that disabling birdseye for a previously enabled camera that has had a last_active_frame wouldn't get cleared. So there is some logic to zero out the last active frame which works... But is this how it should be done? https://github.com/blakeblackshear/frigate/compare/dev...sberryman:frigate:sberryman/mqtt-birdseye-mode?expand=1#diff-032726a7034bcbf31b308cd4452c695b71839494197d463764e5389604af23efR590-R596
3. Topics: Does this match the standard you are using right now? I tried to copy it but could have made a few mistakes.

This is a solution for issue #3244

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[sberryman]

@NickM-27 I know you just approved this so I want to give you a heads up. There were two lines that were commented out in dispatcher that shouldn't have been in there.