fix: process http over https proxy correctly

[barjin]

Previously, HTTP request (http://example.com/resource) over HTTPS proxy (https://proxy.com) was sent as:

• HTTP GET -> https://proxy.com/example.com/resource.
  • this causes errors, as we're sending an HTTP request to an HTTPS proxy.

After a discussion with @jirimoravcik , we figured that the "pathname" proxies are a marginal thing (CONNECT is more popular nowadays).

This PR fixes that - got-scraping now does:

• HTTPS CONNECT -> https://proxy.com/ -> HTTP GET http://example.com/resource.

  Yet, there is still this comment: // Upstream proxies hang up connections on CONNECT + unsecure HTTP maybe @szmarczak knows what that was supposed to mean? 😅 seems dangerously close to what we want to do now.

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Fixes #126

[barjin]

Huh, so the description of this PR mentions the existence of "no-CONNECT" proxies. I'm not sure whether there is an easy way of determining whether a proxy supports the CONNECT method (an easy way other than a preflight CONNECT request).

[barjin]

As discussed w/ @B4nan, we'll go through with this - there is no repro to be found for the "no-CONNECT" proxies - worst case, we can always revert (and we'll have the actual repro by then :))