Worker-name identity token

[tazlin]

The general idea would be:

• Worker starts.
• Worker generates a random token and saves it to disk
• Worker does first jobpop and uses the token in the payload/header
• API saves the token to the worker name in the db
• API now requires the random token to be presented when doing jobpops with this worker name for the next 5 minutes (or some other suitable interval).

This would give more resiliance to certain schemes such as automatically starting workers in a cloud environment without having to rely too heavily on worker name management on the client side to avoid name collision.

A couple of notes:

• This should be entirely optional
• The token hash should be returned on the various /v2/workers/* endpoints
• There should be a PATCH/DELETE field/endpoint to remove the token
• The token should automatically expire - the point isn't security, the point is to prevent worker name collisions.