Updated providers.json with complete YouTube schema

[HammyHavoc]

Previously only included YouTube Shorts.

The only thing I'm uncertain about is that when I tried to add "discovery": true to the "endpoints", Synapse didn't want to start with that included. Perhaps someone can shine some light on that?

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[CLAassistant]

All committers have signed the CLA.

[anoadragon453]

@HammyHavoc do you have an example of this improving URL previews for those URLs?

[HammyHavoc]

@HammyHavoc do you have an example of this improving URL previews for those URLs?

Schema is from https://oembed.com/providers.json