This PR adds a minimum set of Helm tests for the Helm chart.
It's heavily based on the approach in [1], but uses a golden-files-based approach instead.
It also runs helm template directly instead of importing the entire Kubernetes API.
Golden files can be updated by running go test ./helm/tests -update or by running make update-golden-files.
[1] https://github.com/coder/enterprise-helmFixes#6552
Cian Johnston