SNMP Alarm Support

I'm a bit nervous about the index values - I think it's going to be increasingly difficult to add new components, because if (say) we add Gemini alarms, we're going to have to figure out the next unused index number. And if we miss a repository (say, we choose 1500 but don't notice that Chronos already has it), I suspect it would cause odd bugs.

In https://github.com/Metaswitch/clearwater-sas-resources/blob/master/clearwater_sas_resource_bundle.yaml we don't have the problem because it's all in one file. Would it be better to take a similar approach here - combining all the alarm definitions into one file, and maybe having small per-package files to enable/disable sets of alarms (e.g. `/etc/snmpd/enable-sprout-alarms`)?