[Proposal] Enable Lombok.toBuilder annotation flag in ResourceModel template

Start with python/rpdk/java/templates/init/guided_aws/ResourceModel.java, linked in the issue, and inspect how generated ResourceModel annotations are assembled. Resolve whether toBuilder should be enabled by default or exposed as a schema flag, then verify that generated Java models support the requested builder-copy workflow.

Dear team,

I wonder if you folks would have any concerns about enabling toBuilder attribute for Lombok @Builder by default or with an additional schema flag?

At the moment, ResourceModel template generates non-parametrized @Builder: https://github.com/aws-cloudformation/cloudformation-cli-java-plugin/blob/master/python/rpdk/java/templates/init/guided_aws/ResourceModel.java#L20

One of the reasons I would like to see this flag enabled is a significant simplification of overriding massive resource model definitions in testing, especially in testing an UpdateHandler.

Here is an example:

public class AbstractTestBase {
  protected static final ResourceModel MODEL_BEFORE;
  protected static final ResourceModel MODEL_AFTER;

  static {
    MODEL_BEFORE = ResourceModel.builder()
      .foo("foo-before")
      .bar("bar-before")
      .baz("baz-before")
      .build();
    MODEL_AFTER = ResourceModel.builder()
      .foo("foo-before")
      .bar("bar-before")
      .baz("totally-different-baz")
      .build();
  }
}

Assume I'm using these models in UpdateHandler test suite. If the update flow has a broad branching based on model attribute invariants, one has to initiate separate model instances for each branch case. It's completely fine for a 5-10 attribute models, but the burden of carrying things around grows once one has to deal with a 30-50 attribute model.

Having toBuilder = true enabled in ResourceModel definition would let one define models like

public class AbstractTestBase {
  protected static final ResourceModel MODEL_BEFORE;
  protected static final ResourceModel MODEL_AFTER;

  static {
    MODEL_BEFORE = ResourceModel.builder()
      .foo("foo-before")
      .bar("bar-before")
      .baz("baz-before")
      .build();
    MODEL_AFTER = MODEL_BEFORE.toBuilder()
      .baz("totally-different-baz")
      .build();
  }
}

In fact, being able to override a static model locally within the current test case scope is even better, it could look like:

public class UpdateHandlerTest extends AbstractTestBase {
  //...
  public void handleRequest_SimpleSuccess() {
    final ResourceModel modelWithUpdatedBaz = MODEL_BEFORE.toBuilder()
      .baz("totally-different-baz")
      .build();
      //...
  }
}