Add Kubernetes Helm chart (#448)

[baniol]

What did you implement:

Closes #448

How did you implement it:

This is a basic, non-prod setup, as it lacks some features, like RBAC for etcd and Event Gateway or TLS for etcd.
More details regarding etcd installation https://github.com/coreos/etcd-operator/tree/master/doc/user.
I think the question is if we want to leave the initial implementation like this (just for playing around with EG on K8s), or it should be as much prod-ready as possible at the start.

Currently, there's only one external service (LoadBalancer), exposing both config and events ports. Probably a better options would be to have 2 services with ingress in front. The problem is that events api doesn't expose a health check endpoint.

How can we verify it:

Todos:

• Write tests
• Write documentation
• Fix linting errors
• Make sure code coverage hasn't dropped
• Provide verification commands / resources
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: YES
Is it a breaking change?: NO

[codecov]

Codecov Report

Merging #484 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #484   +/-   ##
======================================
  Coverage    71.2%   71.2%           
======================================
  Files          37      37           
  Lines        2195    2195           
======================================
  Hits         1563    1563           
  Misses        571     571           
  Partials       61      61

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[mthenw]

@baniol wow, thanks for your contribution. @sebito91 is more familiar with k8s ecosystem and he will review it.

[sebito91]

@baniol I think this is wonderfully done, thank you very much for your contribution! We're in the process of flushing this out internally but I'll gladly accept and merge this PR.

Can you please rebase your code against the latest changes? Once that's that done we can merge.

Once again thank you very much for the contribution, it'll help to have both helm and CRD versions defined in our infra moving forward!

[sebito91]

Think this is excellent work, definitely helps to have a helm chart to assist with deploying the gateway.

If you can please rebase the code we'll gladly merge the PR.