Add configurations for grace period and graceful shutdown timeout

[hnakamur]

What is the problem your feature solves, or the need it fulfills?

Currently grace period and graceful shutdown timeout are constants and cannot be modified.

This causes unwanted 5 minutes delay before calling Runtime::shutdown_timeout.

Describe the solution you'd like

Add configurations for grace period and graceful shutdown timeout. With these configurations, you can set grace period to 0 and adjust graceful shutdown timeout as you like.

Describe alternatives you've considered

None.

Additional context

None.

[andrewhavck]

Closing this as the change was synced.