End to end test for Service <-> Service communication

[tcnghia]

Expected Behavior

We should have an end to end test with a two Services. One Service HelloWorld serves external request like the current HelloWorld example, while the other service EchoService only serves HelloWorld.

This should test the usages of internal FQDN name {route}.{namespace}.svc.cluster.local that we now added, as well as future mTLS enablement.

Actual Behavior

No such test exists.

[scothis]

The request should originate from a pod with the istio-proxy sidecar installed.

[tcnghia]

@bsnchan it'll be awesome if the internal service Echo can be a gRPC in this setup :)