Add support for custom agent skills via plugins (#2202)

* Add support for custom agent skills via plugins
Update Admin.systemPreferences to updated endpoint (legacy has deprecation notice

* lint

* dev build

* patch safeJson
patch label loading

* allow plugins with no config options

* lint

* catch invalid setupArgs in frontend

* update link to docs page for agent skills

* remove unneeded files

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Co-authored-by: shatfield4 <seanhatfield5@gmail.com>