✨(backend) Contract endpoint: download

[rlecellier]

Feature Request

We need a endpoint that return the download url of a contract.

[rlecellier]

I think that this download url could be part of the Contract get/list serializers.
All user that request contract or contract list will want to be able to download it, and this is not restraint by any ability.

[jbpenrath]

Indeed, but I don't think we want to store this link within Joanie database so we will have to retrieve the link from signature provider. That's why I imagined a dedicated endpoint to retrieve this download link instead to retrieve this information on each get/list requests.