CI/CD: Improve testing on charts

[jhmarina]

What needs to be done

Automatic testing of non-trivial chart-based deployments of the s3gw

This should improve our confidence in the usability of the chart and ensure that common deployment scenarios work as intended. These tests should therefore be executed whenever the chart changes or when a release is prepared.

Acceptance Criteria

• Automatic deployment of the s3gw via the chart in case the chart changes
• Automatic deployment of the s3gw via the chart as part of the release pipeline

Additional Information

Currently the chart is only tested in a very minimal configuration, which exercises only a small portion of the templates and does not cover integration with external components, like the certificate manager. While we do have tests that ensure the chart always generates valid templates, we don't test whether these templates deploy a sane configuration and whether the resulting deployment really ends up healthy.

### Tasks
- [ ] Charts: Expand unittest coverage

[jhmarina]

This issue may overlap a bit with https://github.com/aquarist-labs/s3gw/issues/567

[giubacc]

FYI: Imported the repo of the environment: https://github.com/aquarist-labs/s3gw-acceptance A first implementation of some test is already in place. Tests can be extended to cover much more obviously.

[jhmarina]

This is in progress but will span over several Milestones.