Update k8s.gcr.io/external-dns/external-dns Docker tag to v0.15.0

Author: renovate[bot]

manifests/external-dns/values.yaml

@@ -8,7 +8,7 @@ external-dns:
   image:
     registry: k8s.gcr.io
     repository: external-dns/external-dns
-    tag: v0.14.2
+    tag: v0.15.0
   provider: rfc2136
   rfc2136:
     host: "192.168.1.20"