Add admin frontend with `react-admin` and fix the set backend

[jellehuibregtse]

As I promised, the #43 and #87 have been resolved. I would appreciate if everyone could review this one, seeing as it is quite big. There are a few issues that still need to be tackled (as always) and improvements can still be made. Below is a changelog:

• [x] Create a React App from using CRA with react-admin.
• [x] Add prettier and eslint configuration for the admin frontend.
• [x] Wrote a custom data provider to map react-admin to our API.
• [x] Renamed cardSet to set (plural: sets).
• [x] Fix issue where if tag filter was empty it would still not return those cards (this works for sets now too).
• [x] Add CRUD operations for card, set and tag to the admin frontend.
• [x] Using react-admin i18n I added i18n for the admin frontend (currently only Dutch and English). This should still be improved upon by adding the custom translations.
• [x] Fix set entity by adding relation to tag and fix relation to cards. I also added the tag filter for sets.
• [x] Fix set DTOs and add proper swagger documentation for them.
• [x] Add pagination to the findAll for sets.
• [x] Rewrite all tests for the set controller. I also added some more tests for some uncovered lines and branches. Of course, we now have 100% test coverage again.
• [x] Add CI pipeline for the admin frontend.
• [ ] Add custom translations (i18n) for admin frontend.
• [ ] Support more react-admin filters, such as sort (ASC and DESC) and filter.
• [ ] Support getMany and getManyReference in our API, so react-admin can use it.
• [ ] Allow admin to upload .csv or .excel to import cards. (#112)
• [ ] Add favicon to the application.

To see what it looks like, here are a few screenshots:

All react-admin is translated in English and Dutch:

Adding (or updating) a card:

Closes #43, #87