Add $urltransform modifier support

[slavaleleka]

should be trusted

related: AdguardTeam/CoreLibs#1364

[ngorskikh]

Please make sure that $urltransform rules can only modify the path and query part of the URL, we've already had to deal with that in CoreLibs :)
Example:

$urltransform=/\//@evil.org/

Might redirect a request to https://example.org/ to https://[email protected] if you're not careful.

[ngorskikh]

And... now they want the ability to change the origin :)
But only in a very specific case:

1. The pattern part of the rule must start with ^http, verbatim.
2. The URL replacement must be done via an HTTP redirect, not by modifying the outbound request.