Create datadog_outlier_alert

[ojongerius]

To support https://www.datadoghq.com/blog/introducing-outlier-detection-in-datadog/

Example outlier:

{'created_at': 1444197633000,
 'id': 294219,
 'message': 'outlier alert @ojongerius@atlassian.com',
 'multi': True,
 'name': 'outlier alert',
 'options': {'no_data_timeframe': 2,
  'notify_audit': False,
  'notify_no_data': False,
  'renotify_interval': 0,
  'silenced': {},
  'timeout_h': 0},
 'org_id': 27014,
 'overall_state': 'OK',
 'query': "avg(last_5m):outliers(avg:system.cpu.user{*} by {service_name},'dbscan',3.0) > 0",
 'tags': [],
 'type': 'query alert'}