Add option for 4:4:4 chroma subsampling

[bno1]

Currently, the video stream uses 4:2:0 or 4:2:2 chroma subsampling, which means that color information gets downscaled during encoding and upscaled during decoding. This causes sharp changes in colors to appear fuzzy on the client device. A more detailed explanation of chroma subsampling can be found here: https://www.rtings.com/tv/learn/chroma-subsampling.

This is very visible on colored text, colored icons and colorful pixel art. This issue was mentioned before, but not much was discussed about it: https://steamcommunity.com/groups/homestream/discussions/0/485623406959914227/#c485624040225388643

The solution would be to use 4:4:4 chroma subsampling for the video stream, which keeps the color information at full resolution, bringing the stream quality very close to native quality as long as the network can handle it.

Of course, this should be optional as there are disadvantages to using it:
- Higher bandwidth usage and possibly higher latency because of the extra information in the video stream.
- If the bandwidth usage exceeds what the network connection can sustain the video quality will drop significantly, causing compression artifacts that are much worse than 4:2:0 chroma subsampling.
- Hardware encoders/decoders might not support it. I think the software encoder/decoder (libavcodec if I'm not mistaken) already supports this.

Of course, not all users notice this problem and it's barely visible in some games. But I think some users would greatly appreciate an option to enable 4:4:4 chroma subsampling.

[hammerhals]

Yep, I'm the Readyperson for this.