Update JXL preview to rely on helmfile

We'd like to use nuxeo/nos-helmfile repository to describe preview environments.

in nuxeo/nos-helmfile:

• Create pipeline to release `nuxeo/nos-helmfile`
• Create Docker image to embed Helmfile release
• Align Makefile and Docker image to rely on nuxeo/jxlabs-nos-jxl-base-image as base image
• Configure `updateBot` to automatically do a PR for updating base image version

In nuxeo/nos:

• Update nuxeo/nos Chart to apply our helmfile at pre-install; and destroy on pre-delete. Ideally we would nee to map as much as possible helm hooks.

Ideas:

• Review local nos-helmfile Makefile to pass environment using template~<env> pattern.
• Improve the current `nos-helmfile` to deploy resources in multiple namespaces. It can be interesting for sharing a postgresql instance into multiple previews.