Install the developement depedencies before building Etherpad lite to be able to build the admin UI, listen to notifications for handlers

[nono-lqdn]

Hello,

This pull request introduces two changes ;

1. We are now installing the development dependencies, regardless of the NODE_ENV, because following the issue at Building of the admin UI in production is not possible ether/etherpad-lite#7040 , we need them to build the admin UI, even if we are in a production environment.
2. To be able to do this and build Etherpad-lite when the cloning of the git repository has changed files, we are now using the listen keyword to be able to run two handlers.
   2.1 We've also clarified that the cloning of the git repository is not forced, which was the case before.

This pull request complements #108

[0x46616c6b]

I would simplify that:

The notifier should install devDependencies, build Etherpad, and remove the devDependencies. The variable etherpad_node_environment should only be used for the systemd unit to ensure the Node environment is set to production.

[nono-lqdn]

I've included the changes, and update the branch to match main.