[ITV] Overhaul ITV extractor (#30266)

[ITV] Overhaul ITV extractor (#30266)

* support ITVX URLs (thanks Vangelis66)
* support legacy ITV Hub URLs
* include extraction fix 4c57dd2 from sleaux-meaux 3 May 2021
* include extraction fix 6fbcc16, fix by staubichsauger & pukkandan
* work-around duration parsing pending fix to utils.parse_duration
* apply default vanilla UA for pages and media to avoid site blocking
* also detect and report `Episode not found` instead of generic 404
* rework ITVBTCCIE with geo-block detection, best effort geo-restriction handling, news article support
* fix tests