GraphQL: Refactor the GraphQL Query and Mutation Tests

The GraphQL query and mutation tests have quite a bit of copy/paste in order to write for all data bases which is good sign that there is room for some refactoring of the test classes.

We can take a:
* GraphQL Pagination tests approach where we hard code the answers so the same code can test all the databases without the need to write specific queries for all the db-s. This might seem like it requires more work due to having to escape many `"` characters, but this can be done with some smart Find + Replace. This also introduces the overhead of keeping the hard coded data up to date.
* REST tests which share the requests across databases, but each database test class writes its own queries to fetch the right answers from the database.