Draft: Add E2E tests

What is done

• E2E Tests are coded
  • Following sylva-units-operator!314 (merged), a Kind cluster is installed and required CRDs are deployed, including FluxCD and the SylvaUnitsRelease operators
  • Since there is no management cluster, management cluster provided resources required for a workload cluster deployment (SylvaUnitsReleaseTemplate and managed-workload-clusters-settings) are created manually
    • The managed-workload-clusters-settings is taken from a existing cluster. It is probably bigger than required. Optimization could be done
  • A SylvaWorkloadCluster is deployed, then the presence of associated SylvaUnitsRelease is tested
    • It includes OCI and Git repo valuesFrom
  • Resources are then deleted
  • HOWEVER, since the cluster type is workload cluster, not preview, the SUR is not installed properly
• CI Is modified accordingly
  • E2E test is a manual job, which is not launched automatically except when tags are applied
• Improve Renovate
• Bump linter version and fix related issues

Some details

The E2E tests are relying on

• SylvaWorkloadCluster status to have a Ready field set
• SylvaUnitsRelease status to have a Ready field set
• HelmRelease status to have a Ready field set to true and a Reason being installationSucceed

It will be possible to test further (for example sysla-units-status) once preview workload clusters can be deployed. It depends on

• preview values to be added in sylva-core. See sylva-projects/sylva-core!4101 (diffs)
• preview workload cluster type or flag to be available in the SylvaUnitsRelease operator. See sylva-units-operator#44 (closed)