Draft: Support running our processes from within a container
Be it flatpak, docker or ssh, at times we'll want to run processes that
need specific tooling. This could be something including
flatpak-builder --run, docker run or any similar command.
The intent here is to make kate more flexible and able to run such processes.
Draft because this is a Proof of Concept for implementing this. It's unclear to me how we'd fit into Kate's UI this value so there's not much use in merging just yet. This should be set I guess by either a plugin or some configuration file à la vscode.