NUT experimental support

[gsanchietti]

Some users requested the UPS support using NUT software. This is a requested feature especially for NethServer 7 installation than needs to be migrated to NethSecurity 8.

Proposed solution

Since NUT configuration is not trivial and hard to support for the helpdesk, add the feature as experimental:

• add NUT packages: packages can be installed manually and will not be part of the image
• NUT configuration can be done via command line
• NUT will not be officially supported on machines with a subscription

[gsanchietti]

Test case

• Follow the instructions on the temporary admin manual: https://nethsecurity-docs--135.org.readthedocs.build/en/135/ups.html
• Make sure you can install the required packages, by executing the followings steps:
  • https://nethsecurity-docs--135.org.readthedocs.build/en/135/ups.html#step-1-install-the-required-packages
  • https://nethsecurity-docs--135.org.readthedocs.build/en/135/ups.html#connect-to-remote-nut-server (only point 1)