feat: add private_model_server_enabled to in Endpoint.proto (googleapis#31516)

* feat: add private_model_server_enabled to in Endpoint.proto

PiperOrigin-RevId: 806366860

Source-Link: googleapis/googleapis@69e69bf

Source-Link: https://github.com/googleapis/googleapis-gen/commit/c537c4e9b57930a42255416a822ed3de941b43dc
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google-cloud-ai_platform-v1/lib/google/cloud/aiplatform/v1/endpoint_pb.rb

@@ -150,6 +150,9 @@ module V1
         #     Optional. Configuration for GenAiAdvancedFeatures. If the endpoint is
         #     serving GenAI models, advanced features like native RAG integration can be
         #     configured. Currently, only Model Garden models are supported.
+        # @!attribute [rw] private_model_server_enabled
+        #   @return [::Boolean]
+        #     If true, the model server will be isolated from the external internet.
         class Endpoint
           include ::Google::Protobuf::MessageExts
           extend ::Google::Protobuf::MessageExts::ClassMethods