spec-meta-deposit.rst

This includes:

- dropping the old swh.deposit.auth module which included a basic
  authentication middleware. We now use djangorestframework's (drf).
  We did not prior to this due to some package version issue.

- As this returns json response in failing authentication though, we
  convert the response into an swh-deposit one (that code remained in
  the swh.deposit.auth module)