Merge branch 'use-policy-sync-for-external-dns-in-review-apps' into 'master'

Specify the 'sync' policy for the external-dns deployments

See merge request gitlab-org/gitlab-ce!23912

scripts/review_apps/review-apps.sh

@@ -227,7 +227,8 @@ function install_external_dns() {
       --set aws.zoneType="public" \
       --set domainFilters[0]="${domain}" \
       --set txtOwnerId="${KUBE_NAMESPACE}" \
-      --set rbac.create="true"
+      --set rbac.create="true" \
+      --set policy="sync"
   fi
 }