NE-1323: Add default to AWS credentials field

By adding a default value to the spec.provider.aws.credentials field,
it enables the configuration of spec.provider.aws.assumeRole for an
OpenShift user that doesn't need to explicitly specify the credentials
field. Otherwise, an OpenShift user must manually insert "" as the
credentials name to use the assumeRole field.

api/v1beta1/externaldns_types.go

@@ -255,6 +255,7 @@ type ExternalDNSAWSProviderOptions struct {
 	// for more information.
 	//
 	// +kubebuilder:validation:Required
+	// +kubebuilder:default:={"name":""}
 	// +required
 	Credentials SecretReference `json:"credentials"`
 
@@ -491,7 +492,7 @@ const (
 )
 
 type ExternalDNSAWSAssumeRoleOptions struct {
-	// arn is an AWS role ARN that the ExternalDNS
+	// arn is an IAM role ARN that the ExternalDNS
 	// operator will assume when making DNS updates.
 	//
 	// +kubebuilder:validation:Required