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)

• Legacy redirects, part 1 gnomad-deployments#1
• Adds a set of kustomizations for the gnomad blog gnomad-deployments#2
• Add kustomization for ERB deployments exome-results-browsers#89
• Import reads deployment gnomad-deployments#4
• adds kustomizations for a base demo, a modified demo, and the prod ingress gnomad-deployments#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!