[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