code: def _find_usage_api_keys(self):
          
          logger.debug('Finding usage for API Keys')
          key_count = 0
          paginator = self.conn.get_paginator('get_api_keys')
          for resp in paginator.paginate():
              key_count += len(resp['items'])
          self.limits['API keys per account']._add_current_usage(
              key_count, aws_type='AWS::ApiGateway::ApiKey'
          )
docs: Find usage on API Keys.
          Update `self.limits`.