services: add channelz protos (#4191)

This adds the proto and generated output.

These options are used:
option java_multiple_files = true;
option java_package = "io.grpc.channelz.v1";
option java_outer_classname = "ChannelzProto";
diff --git a/services/src/generated/main/java/io/grpc/channelz/v1/GetServerSocketsResponseOrBuilder.java b/services/src/generated/main/java/io/grpc/channelz/v1/GetServerSocketsResponseOrBuilder.java
new file mode 100644
index 0000000..0d618f8
--- /dev/null
+++ b/services/src/generated/main/java/io/grpc/channelz/v1/GetServerSocketsResponseOrBuilder.java
@@ -0,0 +1,69 @@
+// Generated by the protocol buffer compiler.  DO NOT EDIT!
+// source: io/grpc/channelz.proto
+
+package io.grpc.channelz.v1;
+
+public interface GetServerSocketsResponseOrBuilder extends
+    // @@protoc_insertion_point(interface_extends:grpc.channelz.GetServerSocketsResponse)
+    com.google.protobuf.MessageOrBuilder {
+
+  /**
+   * <pre>
+   * list of socket refs that the connection detail service knows about.  Sorted in
+   * ascending socket_id order.
+   * </pre>
+   *
+   * <code>repeated .grpc.channelz.SocketRef socket_ref = 1;</code>
+   */
+  java.util.List<io.grpc.channelz.v1.SocketRef> 
+      getSocketRefList();
+  /**
+   * <pre>
+   * list of socket refs that the connection detail service knows about.  Sorted in
+   * ascending socket_id order.
+   * </pre>
+   *
+   * <code>repeated .grpc.channelz.SocketRef socket_ref = 1;</code>
+   */
+  io.grpc.channelz.v1.SocketRef getSocketRef(int index);
+  /**
+   * <pre>
+   * list of socket refs that the connection detail service knows about.  Sorted in
+   * ascending socket_id order.
+   * </pre>
+   *
+   * <code>repeated .grpc.channelz.SocketRef socket_ref = 1;</code>
+   */
+  int getSocketRefCount();
+  /**
+   * <pre>
+   * list of socket refs that the connection detail service knows about.  Sorted in
+   * ascending socket_id order.
+   * </pre>
+   *
+   * <code>repeated .grpc.channelz.SocketRef socket_ref = 1;</code>
+   */
+  java.util.List<? extends io.grpc.channelz.v1.SocketRefOrBuilder> 
+      getSocketRefOrBuilderList();
+  /**
+   * <pre>
+   * list of socket refs that the connection detail service knows about.  Sorted in
+   * ascending socket_id order.
+   * </pre>
+   *
+   * <code>repeated .grpc.channelz.SocketRef socket_ref = 1;</code>
+   */
+  io.grpc.channelz.v1.SocketRefOrBuilder getSocketRefOrBuilder(
+      int index);
+
+  /**
+   * <pre>
+   * If set, indicates that the list of sockets is the final list.  Requesting
+   * more sockets will only return more if they are created after this RPC
+   * completes.
+   * </pre>
+   *
+   * <code>bool end = 2;</code>
+   */
+  boolean getEnd();
+}