Support compression in federation responses

[babolivier]

Surprisingly we don't support compression on federation traffic (we just ignore compress: true on federation resources).

Should be as simple as:

            federation_resource: Resource = TransportLayerServer(self)
            if compress:
                federation_resource = gz_wrap(federation_resource)
            resources.update({FEDERATION_PREFIX: federation_resource})

here:

synapse/synapse/app/homeserver.py

Lines 222 to 223 in f30bcbd

	if name == "federation":
	resources.update({FEDERATION_PREFIX: TransportLayerServer(self)})