Adding support for socket path

[MaximeHeckel]

Hey 👋

My team and I were trying to spin up lighthouse server on Google Cloud Run instead of GKE (we think that setting up GKE might be a bit overkill for our needs) and wanted to use a Postgres instance on Google Cloud SQL to save our report data.
However since Cloud Run instances are ephemeral, we can't rely on the sqlConnectionURL to connect to Google Cloud SQL (you have to manually whitelist IPs that can initiate a connection to the DB via public IP).
We usually rely on socket paths for our DB connections and were wondering if we could start a PR on this project to allow the lighthouserc.json file to support some socket path options 😄 (we have a PoC working as I'm writing these words)

[patrickhulce]

Sure @MaximeHeckel sounds good, happy to accept a PR! I think testing might be difficult, but we can hopefully figure something out.