enable REv2 streaming client in CI (pantsbuild#9989)

### Problem

We should use the streaming REv2 client in CI as it will eventually replace the polling client. Testing it as part of CI will let us gain confidence that it operates properly.

### Solution

Enable the streaming REv2 client in CI.

### Result

It should run effectively against RBE.

pants.remote.toml

@@ -23,6 +23,9 @@ remote_execution_extra_platform_properties = [
   "container-image=docker://gcr.io/pants-remoting-beta/rbe-remote-execution@sha256:ec94526d1aa0604b7f693a0b1fb224ca7822a0d821ce20dff50ec808cad597b6",
 ]
 
+# Enable the REv2 streaming client.
+remote_execution_enable_streaming = true
+
 # This should correspond to the number of workers running in Google RBE. See
 # https://console.cloud.google.com/apis/api/remotebuildexecution.googleapis.com/quotas?project=pants-remoting-beta&folder&organizationId&duration=PT6H.
 process_execution_remote_parallelism = 32