🌱 Adding CI/CD

This adds the capability for CI/CD in the staging environment. The gitlab-ci.yaml builds an image and pushes it to the gitlab registry. In the second stage the image tag in the values.yaml inside of the manifest directoryl gets updated. ArgoCD in the staging cluster will then sync the new state.

The manifest directory is added, which contains the necessary files to deploy in a Kubernetes Cluster. The ci directory with the kompose generated kubernetes manifests is removed.

Before merge:

• @JohannesL build stage needs to be fixed first
• Testing the CI/CD, because of the failing application build this is not tested
• We need to adjust in the gitlab-ci.yaml the branch names from ci to main.
• Need to wait for final clearance of the subdomain
• Testing API and frontend together - maybe this needs further adjustments in the ingress object and in the env variables of the frontend.
• Add probes (startupProbe, livenessProbe, readinessProbe)
• Rebase & Squash commits