[RFR]  Add PUT and POST api routes

- [x] Add PUT `/checks` route (create a new check)
- [x] Add POST `/checks/:id` route (update a new check)
- [x] Refactor dashboard app to use `populateFromDirtyCheck` instead of `populateCheckFromRequest`
- [x] Add unit tests for `populateFromDirtyCheck` method
- [x] Add functional tests for api routes 
- [x] Return proprer status code (200, 400, 404, 500) for api routes
- [x] Write documentation for api
- [x] Add an example for each route with parameters
- [x] Complete first test : check that the number of elements in response is equal to the number of created fixtures 


Not sure everything is ok (especially for the doc part), but I'd like your opinion on it so I put the status to RFR.