consider improving folder structure

https://pkg.go.dev/github.com/opiproject/sztp/sztp-agent@v0.0.0-20240620011611-33b5b5ce949c/pkg/secureagent

now that I removed the server code from here, we can probably `git mv ./sztp-agent/* ./`

also maybe we can find better name for the package then `pkg/secureagent` ?