Diagnostic cli does not detect proxy like agent does.

The diagnostic cli does not detect the proxy setting on **Windows** the same way as the agent does.
The agent goes through the documented order of methods to read the settings.
But the cli only reads the system environment variables -

**The result is that the diagnostics is not a true reflection of the agent's connectivity.**

I had a look at the code, and it seems like the cli calls _GetProxyConfig_() in https://github.com/aws/amazon-ssm-agent/blob/mainline/agent/proxyconfig/proxy.go
instead of https://github.com/aws/amazon-ssm-agent/blob/mainline/agent/proxyconfig/proxy_windows.go

Compare the diagnostic CLI's call to GetProxyConfig in agent/proxyconfig/proxy.go with the Windows-specific implementation in agent/proxyconfig/proxy_windows.go. Start by tracing how the CLI selects proxy settings, then make its Windows behavior follow the agent's documented order of methods. Done means diagnostics reflect the agent's connectivity settings on Windows.

Written by the indexing model from the issue text.