Pass Go's `time` function into the alertmanager templates to be able to do time calculations

[aboukhal]

Proposal

Currently, it's not possible to do time calculations when sending alerts to Slack for example. Explicitly converting to another time zone or calculating a duration between startsAt and now would be a tremendous help. There is nothing on Slack/Mattermost's side to do any conversions or calculations there.

This would be easily solved by passing the default time functions into the template at this location.

alertmanager/template/template.go

Line 170 in 680568b

var DefaultFuncs = FuncMap{

[grobinson-grafana]

We added date and timezone functions here.

[aboukhal]

This is awesome. Although, since so little from time is passed through, calculations are still not possible.