Extract runtime clients build logic from EvaluateYamlConfig

The following discussion from !1641 (merged) should be addressed:

• @tle_gitlab started a discussion: (+1 comment)

  suggestion (non-blocking): I think EvaluateYamlConfig should be a pure data model representing YAML configuration and not responsible for building/resolving runtime clients. One idea to move this to a helper class/method.

  class ClientResolver:
      """Utility class for resolving clients based on flow configuration."""
  
      @staticmethod
      def resolve_for_config(config: "EvaluateYamlConfig") -> CommonClients:
          """Resolve clients based on the flow configuration requirements.
  
          Args:
              config: The evaluate YAML configuration
  
          Returns:
              CommonClients instance with appropriate clients configured
  
          Raises:
              TypeError: If the flow doesn't implement the required interface
          """
          builder = ClientBuilder()
  
          try:
              # pylint: disable-next=no-member
              if not config.flow.gitlab_connection_required:
                  env = CommonEnvVariables.model_validate({})
              else:
                  env = GitlabEnvVariables.model_validate({})
                  builder = builder.with_gitlab_rest_client()
          except AttributeError as ex:
              raise TypeError("BaseFlowYamlConfig has to be implemented") from ex
  
          return builder.build(env)