Add stub for audio upload endpoint

[iKevinY]

:construction_worker: Changes

Adds a simple POST endpoint at /upload that can accept file uploads. For now, the endpoint just returns some basic information about the uploaded file (ie. name, type, size, and the leading bytes of the file). Closes #46.

:flashlight: Testing Instructions

Build the server and upload a file via a POST request.

$ make build-prod && make run

# Using cURL:
$ curl -i -X POST -F "file=@${PATH_TO_FILE}" http://localhost:80/upload

# Using HTTPie:
$ http -f POST :80/upload file@${PATH_TO_FILE}

The server should respond with some information like this:

{
  "filename": "nature24270.pdf",
  "leading_bytes": "b'%PDF-1.3\\n%\\xc4\\xe5\\xf2\\xe5\\xeb\\xa7\\xf3\\xa0\\xd0\\xc4\\xc6\\n6 0 o",
  "mimetype": "application/octet-stream",
  "size": 7752280
}

---

:hourglass: Status: Open for Visibility :tickets: Ticket(s): #46