Add profiler span for sending the Execute request

We are seeing profiles in which there is a large gap between the start of the `execute remotely` span and the the start of the `queue` span reported by the remote executor. The current theory is that there is contention on the channel with async tasks spawned by `--remote_cache_async` which this span could help pin down.

Closes bazelbuild#25947.

PiperOrigin-RevId: 753068760
Change-Id: I2b004152ab695530d02d160b8c7b446fcc89e60f

Author: fmeum

src/main/java/com/google/devtools/build/lib/remote/GrpcRemoteExecutor.java

@@ -24,6 +24,9 @@
 import com.google.common.base.Preconditions;
 import com.google.devtools.build.lib.authandtls.CallCredentialsProvider;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
+import com.google.devtools.build.lib.profiler.Profiler;
+import com.google.devtools.build.lib.profiler.ProfilerTask;
+import com.google.devtools.build.lib.profiler.SilentCloseable;
 import com.google.devtools.build.lib.remote.common.OperationObserver;
 import com.google.devtools.build.lib.remote.common.RemoteActionExecutionContext;
 import com.google.devtools.build.lib.remote.common.RemoteExecutionClient;
@@ -165,11 +168,15 @@ public ExecuteResponse executeRemotely(
                                     execBlockingStub(context.getRequestMetadata(), channel)
                                         .waitExecution(wr));
                       } else {
-                        replies =
-                            channel.withChannelBlocking(
-                                channel ->
-                                    execBlockingStub(context.getRequestMetadata(), channel)
-                                        .execute(request));
+                        try (SilentCloseable c =
+                            Profiler.instance()
+                                .profile(ProfilerTask.REMOTE_EXECUTION, "send Execute request")) {
+                          replies =
+                              channel.withChannelBlocking(
+                                  channel ->
+                                      execBlockingStub(context.getRequestMetadata(), channel)
+                                          .execute(request));
+                        }
                       }
                       try {
                         while (replies.hasNext()) {