Feature request: run commands on host when connect via ssh

When Postico opens a connection via a ssh connect, it would be nice to have the ability to run first a command on the host.

My use case is to start first the proxy on a Kubernetes cluster: `kubectl port-forward the-pod-with-postgresql 7070:5432 -n namespace`

Start by tracing Postico's SSH connection flow and the handling of the example kubectl port-forward command. Define how a command would run on the host before the database connection, then verify the command completes before connecting; the issue names no files or tests, so repository exploration is required.

Written by the indexing model from the issue text.