Add query delay flag to Prometheus query script. (#31611)
Add query delay flag to Prometheus query script. (#31611)

* Add query delay flag to Prometheus query script.

This PR adds the flag allows user to config the delay of querying
the Prometheus.

* Update the help message of the flag to be more clear.
grpc/grpc,grpc/grpc,grpc/grpc,grpc/grpc,grpc/grpc,grpc/grpc,grpc/grpc,grpc/grpc,grpc/grpc,grpc/grpc,grpc/grpc,grpc/grpc