Find usage on VPC Links. Update `self.limits`.

def _find_usage_vpc_links(self):
        """
        Find usage on VPC Links. Update `self.limits`.
        """
        logger.debug('Finding usage for VPC Links')
        link_count = 0
        paginator = self.conn.get_paginator('get_vpc_links')
        for resp in paginator.paginate():
            link_count += len(resp['items'])
        self.limits['VPC Links per account']._add_current_usage(
            link_count, aws_type='AWS::ApiGateway::VpcLink'
        )