Adds V3 API samples for srvcs, tenant usage, server_diagnostics

Adds V3 API samples for the services, simple tenant usage and
server_diagnostics extensions. Bundling them together to save
on review load

Partially implements blueprint v3-api-unittests
Partially implements blueprint v3-api-specification

Change-Id: I91edc6500acbe92221427383b4bcd3d00a8faadd
Merge "Adds V3 API samples for srvcs, tenant usage, server_diagnostics"