Frontend: Hook up category attribute configuration screen

Load and save categories on the Category attribute configuration screen:

design: #547963[Security_configuration_-_group-level_-_security_labels_-_category_details_-_full_edit.png] 🎨

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• hook the attributes configuration screen up to load real data from the backend - [ ] when viewing this screen from a subgroup, the project counts in the category list should only count projects within that subgroup #575976

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• hook the attributes configuration screen up to save real data to the backend
• required fields to save a category: name, selection type
  - [ ] required fields to save a category: at least one attribute deferred
• once a category has been saved with a selection type, that field cannot be changed
  - [ ] pending changes to a category and/or its attributes are kept as a private/personal draft in localStorage, see this thread 🧵 descoped for now
• clicking the Save changes button makes the changes
• an indicator next to the button shows how many unsaved changes there are - hovering over it shows a list of changes and a Discard changes button that resets the category/attributes to their current state
• show a toast when the changes are saved or discarded

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• add a ⋮ with a Delete action to the upper right corner of categories that can be deleted (fully editable, user-created), clicking the action triggers a confirmation modal, confirmation triggers the category to be deleted by sending the mutation to the backend