allow configuring ports

[dafydd-t]

Some network setups require the PDC agent outbound connections to be forwarded through other hosts or bastions on the way to the PDC infrastrcture. Whilst PDC infracsturcture in Grafana Labs will ultimately be listening on ports 443 and 22, the intermediate hosts may be listening on a different port before forwarding on to port 22.

Make the API and SSH ports that the agent tries to connect to configurable, so we can support this use case.