Add SNMPtrap service

[titilambert]

Hello !
I need to add a SNMPtrap service for alerting.
Are you open to this ?
I think about using this lib : https://godoc.org/github.com/soniah/gosnmp which is the same as telegraf.

Thanks for your answer

[nathanielc]

@titilambert Are you wanting to generate SNMP traps or collect existing traps?

[titilambert]

@nathanielc To generate snmptraps. Does it fit with the roadmap ?

[nathanielc]

@titilambert I am only marginally familiar with how SNMP traps work but it seems like it would be similar to adding a new alert handler and service. There are many existing PRs already that do similar work.

[titilambert]

PR WIP: #929
I'm just starting to get it working.
Need some cleanup and templatingx