External Process Manager

As of now, the custom apps cant say or define their required processes.

For example,
- Mail needs stalwart (but cant manage deployment of it easily)
- Meet needs mediasoup or drive / sheets needs TUN server
- Sometimes users request some way to run other software along with bench

We need these features -
- [ ] Ability to install system packages by defining somehow in custom app
- [ ] Ability to define a process in custom app. Everything should run as systemd service only
- [ ] Show the process info inside the pilot's UI with support for restarting or stop