Create an interface to Deppy that encapsulates the necessary solver methods

[awgreene]

User Story:

• As a developer on the Operator Controller project, I would like to place any calls to Deppy solver behind a reasonable interface so I can easily test or swap out the Deppy implementation.

Background:

• The Deppy project is being developed as a library that third party projects may utilize.
• There is a possibility that the Operator Controller will need to introduce an Kubernetes Native API (a CRD) that will allow users to configure constraints sent to the resolver.
• To support the possible change, calls to the Deppy Solver should be be done through an interface.
• Placing the Solver behind an interface will simplify unit testing as well.
• The existing solver interface can be found here.

Acceptance Criteria:

• The Deppy Solver is implemented using an interface

[perdasilva]

https://github.com/operator-framework/operator-controller/blob/main/internal/resolution/resolver.go is nearly there. I think we should just refactor to remove the entitySource parameter and create that internally in the resolver.