code: def _find_usage_certs(self):
          
          logger.debug('Finding usage for Client Certificates')
          cert_count = 0
          paginator = self.conn.get_paginator('get_client_certificates')
          for resp in paginator.paginate():
              cert_count += len(resp['items'])
          self.limits['Client certificates per account']._add_current_usage(
              cert_count, aws_type='AWS::ApiGateway::ClientCertificate'
          )
docs: Find usage on Client Certificates. Update `self.limits`.