Extend onvif server to support Unifi Protect

[acortelyou]

Resolves #613.

Marking draft pending feedback.

Note: Unifi uses appears to use MAC as unique identifier, requiring bridge network to achieve multiple instances

[AlexxIT]

FrameRateLimit should be integer. Where you get this values?

[acortelyou]

I used tcpdump to compare go2rtc and a working implementation, 29.97 just happens to be the framerate from the NTSC cameras I have.

Bitrate and FPS are displayed in the Unifi Protect web GUI but unclear if exact values are critical to functionality.

The RateControl block is required but I didn't test if FPS comes from there or GetVideoSources.

I figure those values and more should be configurable, but I didn't see an obvious way to extract the information from a stream/producer object.

Unifi Protect also seems unwilling to authenticate over RTSP even when you embed the credentials in the stream uri. I couldn't find where in the onvif spec you're supposed to configure that. The creds are included in each soap request.

[acortelyou]

I did some additional testing.

VideoEncoderConfiguration.RateControl is required to be present but the contents are not.

VideoEncoderConfiguration.RateControl.{FrameRateLimit,BitrateLimit} are optional but they are used as the values shown in the webui, for display only.

VideoEncoderConfiguration.Resolution is what shows in the webui, for display only.

Removing VideoSourceConfiguration seems to break the snapshots for some reason.

VideoSources.FrameRate don't seem to be required, removed.

VideoEncoderConfiguration Quality, Interval, and SessionTimeout don't seem to be required, removed.