[new feature] Support user-level auth in CLI

[jmsktm]

New feature or functionality
Allow / require CLI users to authenticate using a user token for reasons such as security, access control, audit trail maintenance, and abuse prevention etc. This can work in conjunction with the signadot-api-key, which could be useful for the CI path.

For the actual implementation, we could either have the users generate the token via the dashboard, or alternatively, have them authenticate with Auth0 and pass the Auth0 bearer token.

Additional considerations
N/A