input: Write a python function to validate the data in the ChefConf class.
  assert validate_chefconf({'chef_server_uri': 'http://example.com', 'chef_validation': 'pem_data', 'chef_link': True}) == True
  assert validate_chefconf({'chef_server_uri': 'http://example.com', 'chef_validation': '', 'chef_link': True}) == False
  assert validate_chefconf({'chef_server_uri': '', 'chef_validation': 'pem_data', 'chef_link': True}) == False
output: def validate_chefconf(data):
      if not isinstance(data, dict):
          return False
      required_keys = ['chef_server_uri', 'chef_validation', 'chef_link']
      for key in required_keys:
          if key not in data:
              return False
      if not data['chef_server_uri']:
          return False
      if not data['chef_validation']:
          return False
      if not isinstance(data['chef_link'], bool):
          return False
      return True