feat: use custom url for binary download

[n1ru4l]

This solves #338 which unfortunately got closed without being addressed.

This feature is necessary for people that are self-hosting the youtube-dl binary, e.g. on S3

cc @Kikobeats

[Kikobeats]

Hey, @n1ru4l I understand your use case but I prefer to don't add a new environment variable it could be a thing we can avoid.

What we can do to avoid the new environment variable is to check the response content type here:

https://github.com/przemyslawpluta/node-youtube-dl/blob/master/lib/downloader.js#L29

1. If the content type is text, then the body contains the URL for fetching the resource.
2. Otherwise the response is binary.

If you can make that change I will happy to merge :)

[n1ru4l]

That would not work as there are additional get parameter added here:

node-youtube-dl/lib/downloader.js

Line 89 in 6131a9a

`${ENDPOINT}?platform=${isWin ? 'windows' : 'linux'}`,

[Kikobeats]

@n1ru4l not seeing that is an issue since query parameters are ignored by S3 files.

e.g., https://s.microlink.io/kdsy_4QyLo6Kh61e8SOtMcxCtWg_.png?foo=bar&platform=darwin

[n1ru4l]

But it will not append .exe properly?