[Discuss] Adding Core service functionalities to SDK

[mdeutch]

Is your feature request related to a problem? Please describe.
Currently FeastClient provides Serving access only

Describe the solution you'd like

• Implement an abstract class that will handle all channel and stub common functionalities:

  public abstract class StubManager<S extends AbstractBlockingStub<S>> implements AutoCloseable{
      private final ManagedChannel channel;
      protected S stub;
  
      protected abstract S getStub(Channel channel); 
      
      /*
              Include common functionalities to managing channel and stub
       */
      
  }

• create FeastCoreClient with new core functionalities

  public class FeastCoreClient extends StubManager<CoreServiceBlockingStub> {
    ...
  }

  • create FeastServingClient with serving functionalities taken from FeastClient

  public class FeastServingClient extends StubManager<ServingServiceBlockingStub> {
    ...
  }

• Deprecate FeastClient and suggest to use FeastServingClient instead

Describe alternatives you've considered

1. Adding to FeastClient a CoreServiceBlockingStub and a channel and just add on the core functionalities
2. Refactoring FeastClient to be an abstract class that has a list of all core and serving functionalities to be implemented in child FeastServingClient and FeastCoreClient classes

[mdeutch]

Important to mention that I am with Salesforce, my team has opened this issue as well.