Specify that stderr and stdout streams are URIs

In lieu of a more fully fledged service discovery layer, explicitly specify that the stderr and stdout stream names are in fact URIs from which one can Bytestream.Read.

build/bazel/remote/execution/v2/remote_execution.proto

@@ -1224,12 +1224,12 @@ message ExecuteOperationMetadata {
   // being executed.
   Digest action_digest = 2;
 
-  // If set, the client can use this name with
+  // If set, the client can use this URI with
   // [ByteStream.Read][google.bytestream.ByteStream.Read] to stream the
   // standard output.
   string stdout_stream_name = 3;
 
-  // If set, the client can use this name with
+  // If set, the client can use this URI with
   // [ByteStream.Read][google.bytestream.ByteStream.Read] to stream the
   // standard error.
   string stderr_stream_name = 4;