Consume Disputes GraphQL endpoint to add attachments to a specific Dispute

[duranmla]

Currently, our service generates the documents but it doesn't upload these to the Disputes database. The idea is to expose some endpoints we can use from the document service to upload the attachments to the Disputes app. The endpoints will be implemented in debtcollective/disputes#152.

[orlando]

I'll leave this out of the sprint since we are moving forward with the shared model approach.

[duranmla]

In that sense, this feels like "freeze"/"invalid"/"won't do" or something like that type of issue