Add helm chart with initial functional test

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[mkjpryor]

The problem with Django more generally is that the documentation assumes you have one settings file, but there are actually two classes of settings:

1. Those that define the app and should be in the Docker image, e.g. INSTALLED_APPS
2. Those that are genuinely runtime configurations, that should be injected using the chart

In Azimuth, we use https://github.com/stackhpc/django-flexi-settings to allow us to break up the settings file in this way. If we are going to stick with Django, I think it is worth doing something similar here.

[scrungus]

@mkjpryor huh, for some reason when I first tried this I was getting some permissions errors about service accounts, which I can't remember exactly by memory. But removed it now and it still works 🤷