Write tests for helm chart

[batpad]

https://github.com/kubernetes/helm/blob/master/docs/chart_tests.md - this seems like a great way to test - it maybe a bit more complicated for us due to the time taken for the web container to come up. But we should try and write some basic tests to get started. Getting these tests to work on Circle might be another challenge, but let that not stop us from having basic tests that can be run to verify a release works as expected.

cc @Rub21

[batpad]

Bump, cc @geohacker - this would be really really nice to do.

It does seem like #25 makes this a bit tricky, but there are well established practices now to run tests for helm / k8s deploys in CI, generally using k3s to run a lightweight kubernetes cluster, install the helm chart onto it, and have some tests to check that services are working basically as expected.

This will be a bunch of work, but will be great to make a start toward, to at least have basic assurance that our basic use-cases all continue to work, especially when updating upstream code, etc.