test: establish integration tests

[goatfryed]

We don't just want to manually review the generated k8s manifests and optionally manually apply them to a test cluster, but we want to automate this.

As an example of spring-boot, we want to automatically in a pipeline setup a cluster, install the chart with a sane, all encompassing, but minimal configuration and verify general healthyness. We also want to verify our helm test (release tests).

Note that this requires also setup of a dedicated, minimal spring-boot-application

• spring-boot test image
• Define integration test concept
• CICD Integration Test setup
  • consider k3d cluster for test
• Framework
  • investigate go terratest