Build ponos delegated auth

Refs https://redmine.teklia.com/issues/3228

The goal is to generate unique token by ponos task, linked to the process creator user rights: a ponos task should not have an is_internal access anymore (to prevent nasty tasks / security risks).

• add a new DRF authentication plugin that requires a Authorization: Ponos XXX token
• that token is uniquely generated for each task (uuid4 + base64)
• the plugin retrieves the ponos task and finds its creator (through Workflow and Process).
• add the token to the ponos tasks by adding new environment variable TASK_AUTH_TOKEN
  • the default current token should still be sent to support old workers
• allow API access to ponos authenticated tasks for UpdateWorkerActivity and RetrieveSecret