[SURE-9994] Fleet support for SSH proxy servers

[kkaempf]

SURE-9994

Request description:

Fleet support for SSH proxy servers. 

Actual behavior:

Fleet does not clone the github repo behind a proxy server using SSH keys for authentication. 

time="2025-03-25T13:34:06Z" level=fatal msg="dial tcp 20.207.73.82:22: connect: connection refused" 

Expected behavior:

Fleet should support SSH key based authentication with Proxy servers are used. 

Workaround:

Is a workaround available and implemented? yes/no : NA

Additional notes:

I was able to inject few confiurations on the node and a custom container that I created on an RKE2 cluster and able to clone the git repo from github using SSH keys via the proxy server. So, this seems to be a limitation on the Fleet side. 
The proxy server used in this case is Squid Proxy server.