add Audio API support for axis network speakers

[jonoberheide]

Ok, I stepped out of HA-land [1] for a bit to add the Audio API support natively to the axis library.

This PR:

• Adds the skeleton for the Audio API
• Adds the transmit.cgi request to send audio to the speaker
• Adds a ffmpeg helper to transcode any input audio to the right format
• Adds a --audio flag to be able to invoke it and play audio from the cmdline

[1] https://github.com/home-assistant/core/pull/130163

[Kane610]

This is great! I can't promise i can give you feedback within the next.two weeks (busy IRL) but I eagerly want to see this in the integration. Good job!

[jonoberheide]

I may fling some more code over the wall for the Audio Device Control API (for volume control), but no rush on any review!

[jonoberheide]

Added support for the Audio Device Control API. This can control the gain and mute status for output speakers.

https://www.axis.com/vapix-library/subjects/t10100065/section/t10169359/display

The API is a bit kludgy. The GetDevicesSettings returns a huge deeply-nested JSON structure. SetDevicesSetting expects that same structure, even if just tweaking the gain or mute parameters. One approach would be to Get the big structure, modify it, and then Set it, every time you want to change one of those parameters. Another approach, which I took, was to find the minimal JSON fields required for the request to be accepted and Set that. I opened a case with Axis support to see if they have additional guidance.