[PostgreSQL] Use explicit entrypoint for prometheus exporter

It appears having `args:` without `command:` causes some combinations
of kubernetes & container runtimes to not work as expected.

Change-Id: Id9d692632066de410ca5f13bbfe13d1899b93819

postgresql/Chart.yaml

@@ -15,7 +15,7 @@ apiVersion: v1
 appVersion: v9.6
 description: OpenStack-Helm PostgreSQL
 name: postgresql
-version: 0.1.2
+version: 0.1.3
 home: https://www.postgresql.org
 sources:
   - https://github.com/postgres/postgres

postgresql/templates/monitoring/prometheus/exporter-deployment.yaml

@@ -48,7 +48,8 @@ spec:
 {{ tuple $envAll "prometheus_postgresql_exporter" | include "helm-toolkit.snippets.image" | indent 10 }}
 {{ tuple $envAll $envAll.Values.pod.resources.prometheus_postgresql_exporter | include "helm-toolkit.snippets.kubernetes_resources" | indent 10 }}
 {{ dict "envAll" $envAll "application" "prometheus_postgresql_exporter" "container" "postgresql_exporter" | include "helm-toolkit.snippets.kubernetes_container_security_context" | indent 10 }}
-          args:
+          command:
+            - "/postgres_exporter"
             - "--extend.query-path=/queries.yaml"
           ports:
             - name: metrics