[infoq] Add audio only format if available (#11565)
* [infoq] Add audio only format if available
Refactor cookie code into a function.
Renamed formats to http_video, http_audio, rtmp_video
Renamed extract functions to video instead of videos as they return
one or no video.
* [infoq] Rename to _extract_cookies as it more than one
* [infoq] Remove redundant determine_ext
* [infoq] Add comment about hardcoded URL
* [infoq] Use _hidden_inputs instead of messy regex
* [infoq] Probe if audio URL is valid
Make it possible to pass headers to _is_valid_url
* [infoq] Add audio only test