swh.deposit.auth: private api is free from basic authentication

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)