bisect: advertise gzip,deflate encoding when supported

[staabm]

time to fetch the commits..

... before this PR

➜  phpstan-src git:(bisect-gzip) ✗ time php bin/phpstan bisect foo.php  --good=2.1.0 --bad=2.1.46

Fetching commits between 2.1.0 and 2.1.46...
--------------------------------------------

php bin/phpstan bisect foo.php --good=2.1.0 --bad=2.1.46  0.27s user 0.17s system 0% cpu 54.959 total

... after this PR

➜  phpstan-src git:(bisect-gzip) ✗ time php bin/phpstan bisect foo.php  --good=2.1.0 --bad=2.1.46

Fetching commits between 2.1.0 and 2.1.46...
--------------------------------------------

php bin/phpstan bisect foo.php --good=2.1.0 --bad=2.1.46  0.22s user 0.08s system 0% cpu 44.516 total

-> saves ~10 seconds when downloading big responses

[staabm]

we might instead create a PHPStan namespaced HttpClient and re-use the gzip support in all places we currently directly use GuzzleHttp\Client

[ondrejmirtes]

Not a namespaces child class, just a ClientFactory