Update to stable ingress API

CHANGELOG.md

+## Unreleased
+
+* Update to stable ingress API
+
 ## [0.4.0] - 2021-10-20
 
 * Update redis chart to version 15

templates/ingress.yaml

 {{- if .Values.ingress.enabled -}}
 {{- $fullName := include "wordpress.fullname" . -}}
 {{- $ingressPath := .Values.ingress.path -}}
-apiVersion: networking.k8s.io/v1beta1
+apiVersion: networking.k8s.io/v1
 kind: Ingress
 metadata:
   name: {{ $fullName }}
@@ -40,8 +40,11 @@ spec:
       http:
         paths:
           - path: {{ $ingressPath }}
+            pathType: Prefix
             backend:
-              serviceName: {{ $fullName }}
-              servicePort: http
+              service:
+                name: {{ $fullName }}
+                port:
+                  name: http
   {{- end }}
 {{- end }}