Bugfix&Feature: Add pixel format auto-detect for macOS and manual specifying in ffmpeg device input params

[skrashevich]

This pull request introduces support for specifying the pixel format in the ffmpeg device input parameters. This change affects the internal/ffmpeg/device/devices.go file and the README.md file. The pixel format can now be defined using the pix_fmt parameter. This update is particularly useful for macOS devices, as demonstrated in the updated example for macos_facetime in the README.

Example working configuration on latest MacOS:

streams:
  camera: "ffmpeg:device?video=0&audio=1&video_size=1280x720&framerate=30&pix_fmt=uyvy422#video=h264#audio=aac#audio=pcma"

[AlexxIT]

% ffprobe -hide_banner -v error -print_format json -f avfoundation -video_size 640x480 -framerate 24 -i "FaceTime HD Camera"
{
[avfoundation @ 0x7fbabf104080] Selected framerate (24.000000) is not supported by the device.
[avfoundation @ 0x7fbabf104080] Supported modes:
[avfoundation @ 0x7fbabf104080]   1920x1080@[1.000000 30.000000]fps
[avfoundation @ 0x7fbabf104080]   1280x720@[1.000000 30.000000]fps
[avfoundation @ 0x7fbabf104080]   1080x1920@[1.000000 30.000000]fps
[avfoundation @ 0x7fbabf104080]   1760x1328@[1.000000 30.000000]fps
[avfoundation @ 0x7fbabf104080]   640x480@[1.000000 30.000000]fps
[avfoundation @ 0x7fbabf104080]   1328x1760@[1.000000 30.000000]fps
[avfoundation @ 0x7fbabf104080]   1552x1552@[1.000000 30.000000]fps
FaceTime HD Camera: Input/output error

}

% ffprobe -hide_banner -v error -print_format json -f avfoundation -i "FaceTime HD Camera" 
{
[avfoundation @ 0x7fcda3904080] Selected framerate (29.970030) is not supported by the device.
[avfoundation @ 0x7fcda3904080] Supported modes:
[avfoundation @ 0x7fcda3904080]   1920x1080@[1.000000 30.000000]fps
[avfoundation @ 0x7fcda3904080]   1280x720@[1.000000 30.000000]fps
[avfoundation @ 0x7fcda3904080]   1080x1920@[1.000000 30.000000]fps
[avfoundation @ 0x7fcda3904080]   1760x1328@[1.000000 30.000000]fps
[avfoundation @ 0x7fcda3904080]   640x480@[1.000000 30.000000]fps
[avfoundation @ 0x7fcda3904080]   1328x1760@[1.000000 30.000000]fps
[avfoundation @ 0x7fcda3904080]   1552x1552@[1.000000 30.000000]fps
FaceTime HD Camera: Input/output error

}

[AlexxIT]

This code doesn't work