public String getArnNamespace() {
        return arnNamespace;
    }
Get the AWS ARN service namespace of the service.

<p>If not set, this value defaults to the name of the service shape
converted to lowercase. This value is combined with resources contained
within the service to form ARNs for resources. Only resources that
explicitly define the 'aws.api#arn' trait are assigned ARNs,
and their relative ARNs are combined with the service's arnNamespace to
form an ARN.

@return Returns the ARN service name (e.g., "route53").
smithy-aws-traits/src/main/java/software/amazon/smithy/aws/traits/ServiceTrait.java