show client address in server dashboard

[tlxxzj]

this pr is related to issue #3991 , I added "ClientAddr" in struct ProxyStatsInfo and it will be show in server dashboard.

[fatedier]

#4044 (comment)

This is not the expected implementation method, please try to discuss and reach a consensus in the issue first before submitting a PR to avoid wasting time.

https://github.com/fatedier/frp?tab=readme-ov-file#contributing

If you want to add a new feature, please create an issue first to describe the new feature, as well as the implementation approach. Once a proposal is accepted, create an implementation of the new features and submit it as a pull request.

[tlxxzj]

sorry, I'm learning golang, I don't have a deep understanding of golang