GAPIC clients: merge service address and port #1835
Description
It's natural for service address and port to go together - for example, environment variables for emulator hosts from the gcloud command (e.g. PUBSUB_EMULATOR_HOST) includes service address and port in a single value. We should just merge these together to make life easier on everyone.
I'm unsure if this is beta blocking, but I'll proactively mark it as such until further discussion.