Periodic regression testing

[rubenhorn]

To ensure that all features are working, we should perform regression testing on the entire backend:

• [ ] Spin up a temporary Cloud Formation stack and tear it down after the test
• [ ] Create code to test cases on the live backend over HTTP
• [ ] ❓ How to deal with timeouts or partial test fails
• [ ] (Optional) Scheduled workflow on GitHub actions

Depends on #56

[rubenhorn]

Maybe tests can use events (see https://github.com/CollActionteam/collaction_backend/tree/development/event_examples) to get around the Authorizer in the ApiGateway.

[rubenhorn]

State of the database could be bootstrapped directly using python script and DyamoDB SDK.