Use Host header for GET requests made via Envoy
Add support for a proxy URL for the MediaWiki API. Will be used by
I7ca879ce12756aeb24a2ce41c24c68888d070203 in the kubernetes deployment
so that requests to the MediaWiki API are passed through a proxy.
Bug: T276217
Change-Id: Ic161d00bcf55451cf954d996e34bf09ac15ab7f1