fix: Fix hardcoded image for test connection pod and allow to skip the creation of this pod [RHDHBUGS-155] [RHIDP-5558]

[rm3l]

Description of the change

This PR makes the test-connection pod image configurable.
As reported in https://issues.redhat.com/browse/RHDHBUGS-155, the fact that the image is hardcoded can be an issue in air-gapped environments.
Besides that, this PR also makes it possible to disable the creation of this test-connection pod. I've tested it and it doesn't prevent helm test from passing even with no test pod available.

Existing or Associated Issue(s)

• https://issues.redhat.com/browse/RHDHBUGS-155
• https://issues.redhat.com/browse/RHIDP-5558

Additional Information

• Disable the creation of the test pod and run helm test

$ helm upgrade --install my-backstage-1 charts/backstage --set route.enabled=false --set test.enabled=false

$ helm test my-backstage-1
[...]
NAME: my-backstage-1
LAST DEPLOYED: Tue Jan 14 18:28:25 2025
NAMESPACE: my-ns
STATUS: deployed
REVISION: 1
TEST SUITE: None

• Try using a different image and tag

$ helm upgrade --install my-backstage-2 charts/backstage \
    --set route.enabled=false \
    --set test.image.repository=curl/curl-base \
    --set test.image.tag=8.11.1

$ helm test my-backstage-2
[...]
# the test connection should use this image: quay.io/curl/curl-base:8.11.1
NAME: my-backstage-2
LAST DEPLOYED: Tue Jan 14 18:30:19 2025
NAMESPACE: my-ns
STATUS: deployed
REVISION: 1
TEST SUITE:     my-backstage-2-test-connection
Last Started:   Tue Jan 14 18:32:44 2025
Last Completed: Tue Jan 14 18:32:53 2025
Phase:          Succeeded

Checklist

• Chart version bumped in Chart.yaml according to semver.
• Variables are documented in the values.yaml and added to the README.md. The pre-commit utility can be used to generate the necessary content. Use pre-commit run -a to apply changes.
• JSON Schema template updated and re-generated the raw schema via pre-commit hook.
• List tests pass for Chart using the Chart Testing tool and the ct lint command.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud