Load plugins from system confdir (/etc/ranger/plugins)

[amozeo]

ISSUE TYPE

• Bug fix

RUNTIME ENVIRONMENT

• Operating system and version: NixOS 23.11.4315
• Terminal emulator and version: kitty 0.31.0
• Python version: 3.11.6 (main, Oct 2 2023, 13:45:54) [GCC 12.3.0]
• Ranger version/commit: ranger-master v1.9.3-720-gc7777d55
• Locale: en_US.UTF-8

CHECKLIST

• The CONTRIBUTING document has been read [REQUIRED]
• All changes follow the code style [REQUIRED]
• All new and existing tests pass [REQUIRED]
• Changes require config files to be updated
  • Config files have been updated
• Changes require documentation to be updated
  • Documentation has been updated
• Changes require tests to be updated
  • Tests have been updated

DESCRIPTION

This patch makes ranger load plugins from /etc/ranger/plugins

MOTIVATION AND CONTEXT

I wanted to setup ranger plugin system-wide using nixos system configuration, however I noticed that ranger does not load plugins placed in /etc/ranger/plugins
Since ranger already loads configuration from /etc/ranger/rc.conf, I excpected it would load plugins from the same system confdir too. This change fixes that.

TESTING

All test have ran successfully,
I believe this change doesn't affect other areas of the codebase