Request to Attend an Event based on the Event's id

[j1jlee]

Request to Attend an Event based on the Event's id

Request attendance for an event specified by id.

• An authenticated user is required for a successful response
• New attendance exists in the database after request
• Success response includes the eventId, userId, and a status of
  "pending"
• Error response with status 404 is given when an event does not exist with
  the provided id
• Error response with status 400 is given when the current user already has
  a pending attendance for the event
• Error response with status 400 is given when the current user already is
  already an accepted attendee for the event