[watchertv] Add extractor

[McSwindler]

IMPORTANT: PRs without the template will be CLOSED

Description of your pull request and other information

Adds extractor for WatcherTV. Requires login credentials with active subscription. Modified dropout extractor to be a little more generic and extended it to make the watcher extractor. They are identical in their site functionality.

Fixes #

Template

Before submitting a pull request make sure you have:

• At least skimmed through contributing guidelines including yt-dlp coding conventions
• Searched the bugtracker for similar pull requests
• Checked the code with flake8 and ran relevant tests

In order to be accepted and merged into yt-dlp each piece of code must be in public domain or released under Unlicense. Check all of the following options that apply:

• I am the original author of this code and I am willing to release it under Unlicense
• I am not the original author of this code but it is in public domain or released under Unlicense (provide reliable evidence)

What is the purpose of your pull request?

• Fix or improvement to an extractor (Make sure to add/update tests)
• New extractor (Piracy websites will not be accepted)
• Core bug fix/improvement
• New feature (It is strongly recommended to open an issue first)

[McSwindler]

It's probably better to merge these 2 extractors since they are essentially the same but with different domain names. I'm just not sure how to architect that as this is my first foray into yt-dlp contributions.

I made the dropout extractor a little more generic and then extended it to make the watcher extractor. If this is not the correct way to do this, please point me in the right direction.

[pukkandan]

You are on the right track. But inheriting from concrete IEs commonly cause a lot of issues and so we try not to do that. You can create a DropoutBaseIE and DropoutSeasonBaseIE from which the others can be inherited. _VALID_URL, _TESTS, etc should go in DropoutIE, while all the shared code goes inside the BaseIE

Alternatively, a single IE can be made to handle both _VALID_URLs by grabbing the host name from the input URL.

[McSwindler]

I went with the *BaseIE method and believe I've taken care of everything.

Since different _NETRC_MACHINE values are needed, and it doesn't look like the url is passed through any of the initialize methods, I didn't think it'd be possible to have both in a single extractor. Unless I'm missing something.