message: [benchmark] Replace hardcoded number with macro GRPC_TIMEOUT_MS
  This diff doesn't add anything new.
  Define a const/macro for gRPC call's timeout, instead of using hardcoded number.
diff: @@ -26,12 +26,15 @@ use types::{
  use crate::OP_COUNTER;
  +/// Timeout duration for grpc call option.
  +const GRPC_TIMEOUT_MS: u64 = 8_000;
  +
  /// Return a parameter that controls how "patient" AC clients are,
  /// who are waiting the response from AC for this amount of time.
  fn get_default_grpc_call_option() -> CallOption {
  CallOption::default()
  .wait_for_ready(true)
  - .timeout(std::time::Duration::from_millis(8_000))
  + .timeout(std::time::Duration::from_millis(GRPC_TIMEOUT_MS))
  }
  /// Divide generic items into a vector of chunks of nearly equal size.
  