$wgLocalHTTPProxy can be used to configure a reverse proxy
for requests to domains in $wgLocalVirtualHosts. The previous
implementation of using it as a proper HTTP proxy is no longer
supported and has been reverted out of REL1_37 (856da72363d1ba8bf).
It sets the hostname of the request as a "Host" header, scheme as
"X-Forwarded-Proto" and then sets the proxy's scheme, host and port as
those of the request.
Bug: T288848
Change-Id: Ibc3616f5ad925d464d937ab15461a88619c8b7a7