Integrate cdk_nag as additional best practice tests

[fabdy]

See https://pypi.org/project/cdk-nag/ and https://aws.amazon.com/blogs/devops/manage-application-security-and-compliance-with-the-aws-cloud-development-kit-and-cdk-nag/ 

-> Seems a nice way to check for security problems

DoD:

Integrate it into the testing system and gitlab pipeline