This commit adds support for Grafana's new alerting system, Grafana
Alerting. The existing Grafana integration has been modified to
detect the version of the notification through the structure of the
payload body, since the the structure varies by version. Support for
legacy alerting is been continued. Example fixtures have been added
for Grafana Alerting's webhooks.
Tests updated.
Hari Prashant Bhimaraju