Add Helm Support

[nmanoogian]

This PR:

• Adds a make charts target to build a Helm chart tarball
  • We're using kustomize (via the Operator SDK) to build our k8s yaml today and it's difficult to get these resources into separate files without losing our patches.
  • Instead, we're using yq (the yaml equivalent of jq) to extract just the CRD files which need to be placed in a different directory
• Adds a step to our release action to upload the chart tarball to DopplerHQ/helm-charts (hosted as https://helm.doppler.com) and add the file to the index.yaml file

I tested the action from this branch by temporarily modifying the trigger to run on every push. As a result, the current helm chart is available on https://helm.doppler.com so you can actually give it a try if you like!

[nmanoogian]

@ryan-blunden Would have a minute to kick the tires on this and just see if it feels right compared to other charts you've used? It works as I expected but I'm new to Helm