[Dubbo-issue1814][ Baiji-9] Add .xml configuration of graceful close

[jinzeyu0]

What is the purpose of the change

Brief changelog

[Dubbo-1814]" add xml configuration of dubbo.service.shutdown.wait " to ensure gracefully close.

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[jinzeyu0]

The newest commit is the final answer

[chickenlj]

I think there's no harm to provide an extra configuration, besides, it's more reasonable than that on <dubbo:registry />.