Support for alternative sites

Add a new variable “host” or “service”, which would be an identifiable code for sites other than youtube

i.e:

{
  host: string, // Defaults to youtube, See [services list] // <---
  videoID: string,
  category: string, // Optional, defaults to "sponsor". See [the category list]
  categories: string[] // Optional. Use instead of "category" if you want multiple categories. Will look like ["sponsor","intro"]
}

This would allow to later extend the main extension to support LBRY, bitchute, etc.

[ajayyy]

I was thinking of going with the name “service”

[ajayyy]

https://github.com/ajayyy/SponsorBlockServer/pull/215