Improve Makefile-based Hook integration test jobs #965

Acceptance Criteria:

• In each Hooks directory (with existing integrationtests) implement an valid integration-test target: make integration-test
• Review & Update existing documentation regarding "integration-tests": https://docs.securecodebox.io/docs/contributing/integrating-a-scanner/makefile
• There is no longer a general integration-test folder /secureCodeBox/tests/integration/-> all hook related integrationtests are moved

The hook integration tests are currently subobtimal and need to be migrated to the new template and generally improved. This issue is for determining what exactly needs to be done, and, depending on the complexity of the change, either implementing the changes directly or creating new issues for them.

Current status for the different hooks:

• cascading-scans
• finding-post-processing
• generic-webhook
• notification
• persistence-elastic
• persistence-defectdojo
• update-field