private String toLowerCase(String input) {
        return input.toLowerCase(Locale.US);
    }
Generates the schema doc urls based on the resource's {@code @externalDocumentation}
trait. This is configurable based on the {@code "sourceDocKeys"} and
{@code "externalDocKeys"} plugin properties.

@see <a href="https://docs.aws.amazon.com/cloudformation-cli/latest/userguide/resource-type-schema.html#schema-properties-sourceUrl">sourceUrl Docs</a>
@see <a href="https://docs.aws.amazon.com/cloudformation-cli/latest/userguide/resource-type-schema.html#schema-properties-documentationurl">documentationUrl Docs</a>
smithy-aws-cloudformation/src/main/java/software/amazon/smithy/aws/cloudformation/schema/fromsmithy/mappers/DocumentationMapper.java