docs: GenAI - Add Rapid Evaluation SDK reference documentation

PiperOrigin-RevId: 623268711

Author: jsondai

docs/vertexai/services.rst

@@ -44,3 +44,8 @@ Vertex AI SDK
  :members:
  :show-inheritance:
  :inherited-members:
+
+.. automodule:: vertexai.preview.evaluation
+ :members:
+ :show-inheritance:
+ :inherited-members: