allow users to provide custom netbox scripts to be automatically registered on startup

[mmguero]

Added to the documentation:

NetBox's functionality can be also extended with custom scripting "to provide a way for users to execute custom logic from within the NetBox UI" (see also the "Getting Started with NetBox Custom Scripts").

When Malcolm's NetBox container [starts up]({{ site.github.repository_url }}/blob/{{ site.github.build_revision }}/netbox/scripts/netbox_init.py), it registers any NetBox scripts (ending with a .py extension) found in ./netbox/custom-scripts/ in the Malcolm installation directory. NetBox scripts can be run and managed in the NetBox UI under Scripts in the Customization menu.

The following warning is quoted from the NetBox documentation:

Only install trusted scripts. Custom scripts have unrestricted access to change anything in the database and are inherently unsafe and should only be installed and run from trusted sources. You should also review and set permissions for who can run scripts if the script can modify any data.

This generic custom script registration code has been adapted from #907 from @PrudhviChanda.

[mmguero]

Tested by:

• Saving the NetBox custom scripts documentation as ./netbox/custom-scripts/NewBranchScript.py
• Starting Malcolm
• Verifying the script was created copied and registered:

  •   docker compose exec -u $(id -u) netbox ls -l /opt/netbox/netbox/scripts/
      total 4
      -rw-r--r-- 1 ubuntu ubuntu 1906 Apr 24 19:59 NewBranchScript.py
      -rw-rw-r-- 1 ubuntu ubuntu    0 Mar 29  2024 __init__.py
    

  • 
• Running the script (after manually creating the "Access Switch" device role the script depends on):
  • 
• Verifying output:
  • 
  •