[extractor/generic] Add extractor-args hls_key and variant_query

[bashonly]

• Add extractor-arg variant_query to passthrough the master m3u8 URL query to its variant playlist URLs (similar to how fragment_query works on fragment URLs)

• Add extractor-arg hls_key for generic m3u8s with AES-128 encryption:

Usage: generic:hls_key=(URI|KEY)[,IV]

# to pass the key URI and IV that will override the values in the m3u8:
--extractor-args "generic:hls_key=https://example.com/hls/key,0x1234567890ABCDEF"

# to pass the key and IV, override the m3u8 values:
--extractor-args "generic:hls_key=1234567890ABCDEF,0x9876543210FEDCBA"

# to pass the key URI and use the IV found in the m3u8:
--extractor-args "generic:hls_key=https://example.com/hls/key"

# to pass the AES key and use the IV found in the m3u8:
--extractor-args "generic:hls_key=1234567890ABCDEF"

# if for some reason you need to only pass the IV, it's possible like this:
--extractor-args "generic:hls_key=,0x9876543210FEDCBA"

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[pukkandan]

• Add extractor-arg variant_query to passthrough the master m3u8 URL query to its variant playlist URLs (similar to how fragment_query works on fragment URLs)

Should these be a single arg? Are there cases where one is needed but not the other?

[bashonly]

Should these be a single arg? Are there cases where one is needed but not the other?

I've seen several cases where fragment_query is needed but not variant_query. On the other hand, every time I've seen that variant_query is necessary, fragment_query has also been needed.

Hypothetically though, one of the two (variants vs fragments) could have query strings (or a lack thereof) that cannot be modified, so I think we should keep two separate args