extra_plugin_paths config ignored

[douglas-raillard-arm]

Describe the issue
The following doc shows some configuration options that are seemingly ignored. They are documented as "possibly picked up by an instrument" so it could make sense, but something like extra_plugin_paths seems like it should be interpreted at the beginning of the loading process.
https://workload-automation.readthedocs.io/en/latest/user_information.html#meta-configuration

Other comments (optional)

The context is adding support to specify plugin packages by Python package name instead of a filesystem path. Filesystem paths are good for user-developed plugins but integrate pretty badly with standard distribution on PyPI. For example, I need to specify that the plugins to load are in lisa.wa.plugins package, regardless of where that sits in the filesystem.