Create a badge achievement

Award a badge to a user. Requires administrator privileges. Successful writes log api_badge_achievement_create with the actor and target ids in the admin API audit log.

Integration Tips:

• user_id: The numeric ID of the user receiving the badge.
• badge_id: The numeric ID of the badge being awarded.
• rewarding_context_message_markdown: Optional personalized message shown in the notification or profile feed to explain why the user was awarded the badge.
• metadata: Optional key/value data stored with the achievement for context.
• If the badge cannot be awarded more than once and the user already holds it, the request is rejected with 409 Conflict, and the conflicting achievement_id is included in the response. A 422 is returned for other request errors.