Update dogfood deployment configuration to consume GSM secrets

Created by: ElizabethStirling

Consume the secrets we just added to the secret manager. We should inject the secrets into the k8s deployment as k8s secrets through a CD step, or through GitHub Actions. K8s env vars should be pulled from these secrets.

Dependencies #17801 (closed)

Useful Links: GitHub action GSM k8s env var from secret

Repository: deploy-sourcegraph-dogfood-k8s-2