Bring back external-dns service account

During CoreDNS refactor https://github.com/AbsaOSS/k8gb/pull/292
local external-dns instance was removed, while Route53 and NS1
external-dns instances relies on service account created by local
instance. This commit brings back external-dns service account.

Fixes: https://github.com/AbsaOSS/k8gb/issues/328

Signed-off-by: Dinar Valeev <dinar.valeev@absa.africa>

chart/k8gb/templates/external-dns/service-account.yaml

@@ -0,0 +1,9 @@
+apiVersion: v1
+kind: ServiceAccount
+metadata:
+  name: external-dns
+  namespace: {{ .Release.Namespace }}
+{{ if .Values.route53.enabled }}
+  annotations:
+    eks.amazonaws.com/role-arn: {{ .Values.route53.irsaRole }}
+{{ end }}