[Task] Add shared service resources to the state store

[deniscep]

Feature: #23

• Modify the state store so that it can store state for the shared services (API)
• resources of type "shared_service"

Does this need a shared service API with create and update?

[jjcollinge]

@deniscep we'd need to ensure we used etag/precondition on writes to the DB to ensure concurrency is managed here. The initial shared resource documents also need adding during bootstrapping/deployment.

[damoodamoo]

Closing as covered in #1239