导入MOCK类型后端服务API

包含无认证的GET方法API定义，后端服务类型为MOCK。

Swagger示例：

swagger: "2.0"
info:
  title: "importMockEndpoint"
  description: "import apis"
  version: "1.0"
host: "api.account.com"
paths:
  '/mock':
    get:
      operationId: "mock"
      description: "mock test"
      schemes:
      - http
      responses:
        "200":
          description: "mock result"
      x-apigateway-request-type: "private"
      x-apigateway-cors: true
      x-apigateway-match-mode: "NORMAL"
      x-apigateway-backend:
        type: "MOCK"
        mockEndpoints:
          result-content: "{\"message\": \"mocked\"}"
securityDefinitions:
  apig-auth-app:
    in: header
    name: Authorization
    type: apiKey
    x-apigateway-auth-type: AppSigv1
  apig-auth-iam:
    in: header
    name: unused
    type: apiKey
    x-apigateway-auth-type: IAM