User-based fixed token authentication

[MorpheusXAUT]

In order to allow for proper integration into external sites and services, the backend needs to support "static" authentication on a per-user basis, for example via "user API tokens".
Users could generate these tokens in their account page and use them to perform actions on their behalf using third-party services (e.g. a community's internal mission tool).

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Tasks

• API token model
• Endpoints for managing API tokens
• Adaption to authentication strategy to accept API tokens and retrieve user from database