Improvements to SignatureRequest and Fax response schemas

[jtreminio-dropbox]

Changes in this PR:

The metadata property has had its schema updated to reflect what you actually get back from the API. Affected schemas are:

• BulkSendJobGetResponseSignatureRequests.metadata
• SignatureRequestResponse.metadata
• TemplateResponse.metadata

The change is:

• C#: From Object to Dictionary<string, Object>
• Java: From Object to Map<String, Object>
• Node: From object to { [key: string]: any }
• PHP: Remains array but typehint is now array<string,mixed>
• Python: From object to Dict[str, object]
• Ruby: From Object to Hash<String, Object>

Additional changes:

• BulkSendJobGetResponseSignatureRequests.test_mode is now non-nullable
• BulkSendJobGetResponseSignatureRequests.expires_at is now nullable
• SignatureRequestResponse.test_mode is now non-nullable
• SignatureRequestResponse.expires_at is now nullable
• FaxResponse.transmissions is now non-nullable
• FaxResponse.subject is now nullable
• FaxResponse.message is now nullable
• FaxResponse.final_copy_uri nullable string has been added
• FaxResponseTransmission.sender removed

---

This PR fixes a bug with the BulkSendJobGetResponseSignatureRequests schema. It inherits all of the properties in the SignatureRequestResponse schema, but the metadata definition causes problems when SDKs are being generated.

To solve this, I've added metadata to BulkSendJobGetResponseSignatureRequests.

More details:

Fun fact! You can define a property as a key:value (aka javascript object or python dict type) in OpenAPI as follows:

metadata:
    description: 'The metadata attached to the template.'
    type: object
    additionalProperties: {}

This makes the shape of metadata as { [key:string]: any } which is what we want for metadata because it can be any shape a customer decides as long as the key is a string.

We can also define a schema as extending another schema which allows it to inherit all the parent schema's properties, as so:

BulkSendJobGetResponseSignatureRequests:
  title: BulkSendJobGetResponseSignatureRequests
  type: object
  allOf:
    -
      $ref: '#/components/schemas/SignatureRequestResponse'
    -
      properties:
        bulk_send_job_id:
          description: 'The id of the BulkSendJob.'
          type: string

However, there's a bug with the openapi-generator tool when generating SDKs where if a schema extends another using allOf, and the parent schema has a property of type: object, the final type of that property in some SDKs is wrong.

• In Typescript we expect { [key: string]: any } but it actually generates object which is technically not wrong but incorrect all the same.
• PHP: Expect array<string,mixed> but get array
• C#: Expect Dictionary<string, Object> get Object
• Java: Expect Map<String, Object> get Object
• Python: Expect Dict[str, object] get object
• Ruby: Expect Hash<String, Object> get Object

The solution is to add the property to the child schema:

BulkSendJobGetResponseSignatureRequests:
  title: BulkSendJobGetResponseSignatureRequests
  type: object
  allOf:
    -
      $ref: '#/components/schemas/SignatureRequestResponse'
    -
      properties:
        bulk_send_job_id:
          description: 'The id of the BulkSendJob.'
          type: string
        metadata:
          description: 'The metadata attached to the signature request.'
          type: object
          additionalProperties: {}