Add unit tests for the Helm Chart

[scholzj]

We should try to add some unit tests for our Helm chart - for example using the https://github.com/helm-unittest/helm-unittest project.

[scholzj]

Triaged on the community call on 4.4.2024: Makes sense and would be a good contribution for someone who knows / uses Helm.

[maciej-tatarski]

Hi @scholzj, I'm thinking about picking it up. I'm just wondering what should be granularity of the test, do we only want to test more complex scenarios when we use some helm functions and such or do we want to test all the functionalities?

Do we want to have it run on PR as well?

I've create this PR, as a conversation starter. If it is ok for you to do it in this way, I can add the rest of the test to it: #10192

Example pipeline/workflow:
https://github.com/strimzi/strimzi-kafka-operator/actions/runs/9366458701/job/25783959894?pr=10192