✨ (New Backend) GraphQL SQL implementation

[Markus99at]

• add missing sql implementation (currently marked as todos)
• verify the graphql endpoint works using either arangodb or sql
• for now the testdata provider will be used for testing but ideally this should also be adjusted to some predefined custom docker image which already holds test data

[uberroot4]

Before proceeding with the sql implementation the tests agains the existing db must succeed so we know its working as expected.