This commit adds contact point testing to ngalerts via a new API
endpoint. This endpoint accepts JSON containing a list of
receiver configurations which are validated and then tested
with a notification for a test alert. The endpoint returns JSON
for each receiver with a status and error message. It accepts
a configurable timeout via the Request-Timeout header (in seconds)
up to a maximum of 30 seconds.
* Alerting: Implement /status for the notification system
Implements the necessary plumbing to have a /status endpoint on the
notification system.
* Add API examples
* Update API specs
* Update prometheus/common dependency
Co-authored-by: Sofia Papagiannaki <sofia@grafana.com>
