helm: standardize yaml configuration (#15728)

- move application variables under `mastodon` namespace
- restore standard yaml structure for ingress configuration
- move values.yaml.template to values.yaml

chart/templates/service-streaming.yaml

@@ -7,7 +7,7 @@ metadata:
 spec:
   type: {{ .Values.service.type }}
   ports:
-    - port: {{ .Values.application.streaming.port }}
+    - port: {{ .Values.mastodon.streaming.port }}
       targetPort: streaming
       protocol: TCP
       name: streaming