[Feature Request] Allow searching for plugins in system paths

[orowith2os]

Validations

• I have checked for similar feature requests and could not find any.
• I have made sure this is not an already-existing feature.

Description

From what I can tell, Session currently only searches for the plugins in the user paths. If there's a system path for it, I can't see any in the logs, and a quick search over the source code doesn't show anything I recognize.

Suggested solution

Allow setting the path to search for system plugins with at build-time, and maybe have an environment variable to override it for debug purposes.

Session should search the user plugin directories first, then the system paths - if there are any conflicting plugins, prioritize the user plugin.

Alternative solution

No response

Additional Context

This is a blocker for the Flatpak version of Session.