Adds support for multipart/form-data requests in the public api
allowing documents to be uploaded without having to perform a secondary
request.
Need to rollout further endpoints for envelopes and templates.
Need to change how we store files to not use `putFileServerSide`
Extracts the API implementation to a package so we can
potentially reuse it across different applications in the
event that we move off using a Next.js API route.
Additionally tidies up the tokens page and form to be more simplified.
Lucas Smith
David Nguyen
Catalin Pit