Implement the GET endpoint for getting set by id

Setup raml-file and entities for new set items CRUD functionality.
Implement the endpoint which accepts set id and returns the set entry.
Request url: /set/

{set_id}
Request method: GET
Response example: { "id" : "8772b95a-a006-419d-a367-3bd8e36918df", "name" : "1", "description" : "", "setSpec" : "", "createdDate" : "2020-06-24T08:05:24.129+0000", "createdByUserId" : "efa0ceef-32b9-409c-a6c5-2f74c62f6cf8", "updatedDate" : "2020-06-24T08:05:24.129+0000", "updatedByUserId" : "efa0ceef-32b9-409c-a6c5-2f74c62f6cf8" }

acceptance criteria:
- when Get by id and item with such id exists then item is returned
- when Get by id and item does not exist then 404 error returned with error message "Set with id '{set_id}

' was not found"