add jpeg file type for documents

[filnko]

Hi,

as I can't open issues here, I need to open a PR :-)
(this PR shouldn't be merged like this of course)

When requesting documents that the WebSDK uploaded, they have a file_type of "jpeg". The OpenAPI spec however only lists "jpg" as allowed value.
Somehow this should be adapted as your API is not working according to the specification.

Example response from the api:

GET https://api.eu.onfido.com/v3.6/documents/2e503b6a-99c6-4829-802b-9e43903b7c22
{
    "applicant_id": "ce61a2a3-4190-43d2-b634-e7bdabad760b",
    "id": "2e503b6a-99c6-4829-802b-9e43903b7c22",
    "file_name": "document_back.jpeg",
    "file_type": "jpeg",
    "file_size": 2610325,
    [...]
}

Thanks, Christoph

[dvacca-onfido]

@filnko Thanks for your contribution, even though minimal your change looks good to me.

We're going to merge that as it's for now, in future we'll probably remove enum format from file_type property also to align with other endpoints. That can't be done right now since it would cause a breaking change in the libraries.