[stable/superset] Use the target port number instead of a name

Older (but still actual) versions of some Network Policy providers don't support named ports as
a value of `targetPort` field in the Service spec.
Changing it to the number shouldn't break the UX for existing installations.

Signed-off-by: Mikhail Zholobov <legal90@gmail.com>

stable/superset/templates/svc.yaml

@@ -36,7 +36,7 @@ spec:
   ports:
     - name: http
       port: {{ .Values.service.port }}
-      targetPort: http
+      targetPort: 8088
       protocol: TCP
 {{ if (and (eq .Values.service.type "NodePort") (not (empty .Values.service.nodePort))) }}
       nodePort: {{.Values.service.nodePort}}