Introducing support for Aggregate Roots

[einari]

Summary

Adds aggregates to the SDK in a barebones matter, agnostic to whether there is IoC or not.

Added

• System for working with aggregates and aggregate roots
• AggregateOf<> method on Client for creating an aggregate root operation on a specific aggregate
• Small sample showcasing the aggregates system

Changed

• docker-compose in samples run with latest runtime versions