Create helm chart for Kubernetes deployments

[davidsbond]

Currently, the project only provides a kustomize manifest.

1. This isn't particularly useful for customising deployments, you can't template much. So you end up having to do manual changes if you want to use the cert-manager CSI driver for TLS.
2. It's easy to forget to change the image version before you tag a release

Ideally, we should have a helm chart and a CI process that ensures the image version is correct. We can also use helm template in the CI process to produce static manifests for anyone that wants a one-liner.