Adjust Response headers for gzipped body

[mindplay-dk]

If the Response body is unpacked (from gzip encoded content) per the PSR-18 spec:

if a Client chooses to decompress the message body then it MUST also remove the Content-Encoding header and adjust the Content-Length header.

Add (regression) tests as needed.

[mindplay-dk]

Hmm, the Content-Length header cannot be added if the message body is going to be unpacked on the fly via stream filters, as it is now:

https://github.com/kodus/http-client/blob/master/src/HttpClient.php#L111

Unless we block while downloading and unpacking the entire stream to a temporary stream - which seems like a pretty poor performance trade-off just for the sake of adding this header.

Can we just omit the Content-Length header rather than adjusting it?

Or is there some header from which the expected decoded content-length can be obtained?