Prepare indexer storage template

This will allow to run the rpc indexer-storage service in the elastic infra. This does not deploy anything yet.

Refs. swh/infra/sysadm-environment#4780 (closed)

swh/fake-secrets/swh-indexer-storage-postgresql-secret.yaml

+---
+apiVersion: v1
+kind: Secret
+metadata:
+  name: swh-indexer-storage-postgresql-secret
+  namespace: swh
+type: Opaque
+stringData:
+  postgres-swh-indexer-password: fake-swh-indexer-password