add a supergraph configmap option to the helm chart

[garypen]

Here's an example of values.yaml that you could use to mount this to your container:

extraEnvVars:
  - name: APOLLO_ROUTER_SUPERGRAPH_PATH
    value: /data/supergraph-schema.graphql

extraVolumeMounts:
  - name: supergraph-schema
    mountPath: /data
    readOnly: true

extraVolumes:
  - name: supergraph-schema
    configMap:
      name: "{{ .Release.Name }}-supergraph"
      items:
        - key: supergraph-schema.graphql
          path: supergraph-schema.graphql

Note: This takes advantage of the fact that we tpl template the extraVolumes in the deployment template, so {{ .Release.Name }} will be templated into the release name at install. You don't have to do this, you could just hard-code it, but this is neater.

Here's an example command line:

helm upgrade --install --create-namespace --namespace router-test --set-file supergraphFile=supergraph-schema.graphql router-test oci://ghcr.io/apollographql/helm-charts/router --version 1.0.0-rc.9 --values values.yaml

NB: rc.9 doesn't exist, so the command is purely illustrative to show how this works.