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. Revert docs update about
requiring to add empty ("") credentials 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

docs/usage.md

@@ -82,25 +82,6 @@ spec:
     - '{{.Name}}.mydomain.net'
 ```
 
-**Note**: Due to a limitation of the `v1beta1` API requiring the `credentials` field, OpenShift users will be required
-to provide an empty (`""`) credentials field. The empty credentials will be ignored and the secret provided by
-OpenShift's Cloud Credentials Operator will be used:
-
-```yaml
-apiVersion: externaldns.olm.openshift.io/v1beta1
-kind: ExternalDNS
-metadata:
-  name: aws-example
-spec:
-  provider:
-    type: AWS
-    aws:
-      credentials:
-        name: "" # Empty Credentials
-      assumeRole:
-        arn: arn:aws:iam::123456789012:role/role-name # Replace with the desire Role ARN
-```
-
 ## GovCloud
 The operator makes the assumption that `ExternalDNS` instances which target GovCloud DNS also run on the GovCloud. This is needed to detect the AWS region.   
 As for the rest: the usage is exactly the same as for `AWS`.