Add Port Number Option to Installer

[CedricBojoly]

It would be great if the installer could include an option to specify the port number, similar to how it's set up for the homepage LXC container. This would allow the start script to be modified as follows:

pnpm start -p $PORT

I would prefer to use port 80 instead of the default port 3000. With this implementation, users would have the flexibility to either stick with the default port (3000) or change it as needed.

I tested this by modifying the start command in the service file:

ExecStart=pnpm start -p 80

in /etc/systemd/system/homepage.service.

This change worked well for me, and I believe it could benefit others as well.

PS: The port option during installation should be optional, as it depends on the specific application. Not all applications can easily accommodate a different port configuration