Enhance cluster rest proxy to handle content-encoding: gzip responses

[rohitsanj]

We try to always UTF-8 parse responses but fails if the bytes are GZIP encoded. To get it to work right, we should notice the content-encoding, un-GZIP it, do whatever logic we do today, re-GZIP it then send it.

Then can remove Accept-Encoding from the proxy header skiplist.

Test with a request like fetching all the schemas within a cluster.