Support HTTP compression with Java HTTP Client

[kwin]

New feature, improvement proposal

Retrieving both metadata and pom XMLs may benefit from response compression. Maven Central is now on Cloudflare CDN which supports different compression algorithms (https://developers.cloudflare.com/speed/optimization/content/compression/). This should be optionally supported by the different HTTP transports by
a) setting according request headers
b) decompressing the response

[kwin]

This seems to be automatically leveraged by Apache HTTP Client (https://hc.apache.org/httpcomponents-client-4.5.x/current/httpclient/apidocs/org/apache/http/impl/client/HttpClientBuilder.html#disableContentCompression()) unless explicitly disabled. Also Jetty Transporter is already supporting it.