Adds V3 API samples for agents, aggregates and certificates

Adds v3 API samples for the agents, aggregates, and certificates
extensions. Bundling them together to save on review load

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

Change-Id: Iee26fe25b5fd369f2a1f5690ddc095a90526a549
Merge "Adds V3 API samples for agents, aggregates and certificates"