Use Kustomize to manage K8S deployments

[nawatts]

Currently, K8S deployments are managed using manifests and custom wrappers around kubectl (deployctl).

These should be replaced with Helm.

(EDIT: Adding a checklist)

• [x] https://github.com/broadinstitute/gnomad-deployments/pull/1
• [x] https://github.com/broadinstitute/gnomad-deployments/pull/2
• [x] https://github.com/broadinstitute/exome-results-browsers/pull/89
• [x] https://github.com/broadinstitute/gnomad-deployments/pull/4
• [ ] https://github.com/broadinstitute/gnomad-deployments/pull/5
• [ ] browser

[sjahl]

We began rolling out Helm, but the team wasn't happy with all the YAML templating. We decided to pursue a Kustomize-based approach instead. We already have some things that are kustomized, but not everything is, and there's some opportunity to use kustomize more effectively, which is what we're pursuing now!