Assert response against only defined keys.

[melissabillias]

A Scenario like this, will now pass without having to define variable keys like _id.

Actual Response:

[{"email":"email1@test.com","status":"sent","_id":"ee65fa503c664301b9e92c69b8624e6c","reject_reason":null},{"email":"email2@test.com","status":"sent","_id":"d22f4aca0ab94f7f87b38cacfbd30544","reject_reason":null}]

Partial Feature:

    And the response should contain json:                                                          
      """
      [
          {
              "email": "email1@test.com",
              "status": "sent",
              "reject_reason": null
          },
          {
              "email": "email2@test.com",
              "status": "sent",
              "reject_reason": null
          }
      ]
      """