feat: add channel pooling (#9692)

stack-info: PR: #9692, branch: igorbernstein2/stack/5

Author: igorbernstein2

bigtable/bigtable-proxy/src/main/java/com/google/cloud/bigtable/examples/proxy/channelpool/ChannelFactory.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2024 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// Copied from
+// https://github.com/googleapis/sdk-platform-java/blob/a333b0709023c971f12a85e5287b6d77d1b57c48/gax-java/gax-grpc/src/main/java/com/google/api/gax/grpc/ChannelFactory.java
+// Changes:
+// - package name
+// - removed InternalApi annotation
+
+package com.google.cloud.bigtable.examples.proxy.channelpool;
+
+import io.grpc.ManagedChannel;
+import java.io.IOException;
+
+/**
+ * This interface represents a factory for creating one ManagedChannel
+ *
+ * <p>This is public only for technical reasons, for advanced usage.
+ */
+public interface ChannelFactory {
+  ManagedChannel createSingleChannel() throws IOException;
+}