A custom exception `NotesUnavailableException` will be thrown on attempts to load the "admin-note" data store using the `Notes::load_data_store()` method introduced in this PR.
All calls to `\WC_Data_Store::load( 'admin-note' )` were replaced with calls to the above method.
* Add method to enable features
* Add the navigation nudge note
* Add changelog entry and testing instructions
* Update note name
* Fix renamed note class name
* Use redirect to settings instead of directly enabling note
* Remove old feature settings filter