What is the purpose of the change

When using dubbo, developers always need to get dubbo version to debug online problems. And some popular RPC support command to get RPC version like brpc. So I add version command in qos module.

Brief changelog

Add version command in qos module

Verifying this change

When telnet to port of QOS, dubbo version description like "dubbo version "2.7.6" " will return when typing command "version".

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