Add/Update endpoints for kronus server

[Edmond Cotterell]

• POST /users - return user_id/info on user creation
• Return 400 for bad request(e.g db errors like duplicate data or failed constraints) instead of 500
• GET /probes - should work without status filter
• GET /jobs - should work without status filter
• Support Pagination on all endpoints that require it
• GET /users/{id}/probes
• API versioing
• Update docs accordingly