[BUG] user installed plugins are loaded from Headlamp and not AKS desktop

## Bug Description

User plugins are loaded, but from the Headlamp folder and not a separate AKS desktop folder.

- Have some user installed plugins (maybe installed via headlamp, or dev mode).
- Open AKS desktop.
- See custom plugins are loaded.

Not a regression. Also happens with 0.1.0-alpha
Tested on AKS desktop 0.2.0

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- [ ] We want Headlamp and AKS desktop to choose the correct path for plugins. Maybe the backend needs a config to specify path. Perhaps the app/package.json name can be used to determine the path?

Estimate 2 days, needs testing on multiple OS.

Start by tracing how user plugin paths are resolved for Headlamp and AKS desktop, including the backend configuration and app/package.json mentioned in the issue. Reproduce the behavior with a user-installed plugin on multiple operating systems. Done means each application loads plugins only from its own correct folder.

Written by the indexing model from the issue text.