Added extra info to unknown templates

[pradeepbbl]

Currently, we have a very limited number of variable available to the unknown templates which prevent us to match the alert and action notification template (includes incident states) and sometimes unknowns are getting unnoticed due inconsistency (when using external notification systems e.g. pagerduty).

With this patch, I tried to include the alert states to unknown which is very useful when grouping disable using unknownMinGroupSize.

Please let me know your thoughts.

[pradeepbbl]

here is an example of a PagerDuty alert body template

pdMonitoringBody = `{
       "service_key": "XXXXXXXXXXXXXX",
       "event_type": "trigger",
       "description": "{{.Subject | jsonStr}}",
       "client": "bosun",
       "client_url": "{{.Incident}}",
       "incident_key": "AlertName={{.Alert.Name}};IncidentId={{.Id}}"
 }` 

if you make close attention to incident_key we use alert name and incident id combination to reduce duplication. With current unknown template contexts/var, it's impossible for us to prepare an unknown body that matches the above specification and due to this many unknowns are getting unnoticed by teams.

With this patch, we are able to produce the unknown body and post to PagerDuty successfully

pdMonitoringUnknownBody = `{
       "service_key": "XXXXXXXXXXXXX",
       "event_type": "trigger",
       "description": "Alert goes to unknown states",
       "client": "bosun",
       "client_url": "{{ .IncidentUnknownLink .States.Id }}",
       "incident_key": "AlertName={{.Name}};IncidentId={{.States.Id}}"
}`

@kylebrandt / @captncraig could you please let us know your thoughts?

[pradeepbbl]

can this be merged soon :)

[stepashka]

Hey @kylebrandt, @captncraig!
Any objections to this change? Is there something else we need to implement before this gets merged?
Thanks,
Anna