* Add automatic plugin reload
* Refactor builtin/backend
* Remove plugin reload at the core level
* Refactor plugin tests
* Add auto-reload test case
* Change backend to use sync.RWMutex, fix dangling test plugin processes
* Add a canary to plugin backends to avoid reloading many times (#3174)
* Call setupPluginCatalog before mount-related operations in postUnseal
* Don't create multiple system backends since core only holds a reference (#3176)
to one.
