Add NodeJS server as an alternative to PHP

[limaanto]

Problem

I wanted to have an app similar to my_webapp but with nodejs instead of PHP. After hesitating to create a new app, I decided it was better to improve this one instead.

Solution

For this, I added, with the help of @oiseauroch:

• Two entries in the manifest:
  • A choice for the NodeJS version
  • A port (provisionned in any case due to ynh limitations, but this should not matter)
• Services and configs:
  • Systemctl configs to run the NodeJS server
  • A watcher service and path to restart NodeJS upon file update
  • A custom NGinx config because it is incompatible with the default one
• Docs:
  • More info in the description and admin

The install/remove/backup/restore have been adapted and tested. The upgrade script is updated but not tested The change_url script does not change

It is not possible to have both PHP and NodeJS to keep the scripts simple.

PR Status

• [x] Code finished and ready to be reviewed/tested
• [x] The fix/enhancement were manually tested (if applicable)

Automatic tests

Automatic tests can be triggered on https://ci-apps-dev.yunohost.org/ after creating the PR, by commenting "!testme", "!gogogadgetoci" or "By the power of systemd, I invoke The Great App CI to test this Pull Request!". (N.B. : for this to work you need to be a member of the Yunohost-Apps organization)