Support multiple services depending on the same plugin resource

[tedim52]

Currently, kardinal does not handle situations where multiple services depend on the same external / stateful resource managed by our plugin system.

Example, if there are two services (say an API and an Analytics service) that depend on the same AWS RDS plugin system - there's no way to indicate to the kardinal engine that both these services depend on the same service.

This is crucial to address to effectively create flows involving plugins. In this instance, a dev flow should create one dev RDS instance that both the API service and Analytics service now point to.