Several fixes in this commit:
* Added 'namespace' argument, default to 'eshop'.
* Every Helm command (`helm install` and `helm ls` used with `helm delete`) will honor the namespace parameter. This way this script is no longer destructive with the Kubernetes cluster. Usage() has been updated accordingly.
* Custom registry image push didn't honor `--docker-username` and `--docker-password`. A `docker login` has been added to fix the situation.
* AKS DNS discovery was not working properly due to case sensitivity with the JMESPath to the HTTPApplicationRouteZoneName. A small two-entries array with iterative loop has been added ton ensure either way the AKS http routing DNS retrieval is successful.
* Helm charts were enabled to use Kubernetes Ingress, but the `Ingress.spec.rules.host[]` was not honored with the `$dns` variable. This has been fixed in the `helm install` commands and now the script deploys the Ingress as expected.
