Grafana: Feature: Twilio Alerting

[Gui13]

I didn't find any issue regarding this, but I would like to propose a new alerting backend: twilio

I saw that you already have "PagerDuty" filling this space, but this seems like an overkill solution for me ($9/month).
As of today, I'm using a webhook to extract the alert status and send it to my mobile through the Twilio API. It's a simple Flask server with about 20 lines of code.

If I could get rid of it through a specialized Twilio alerting in Grafana, it would be fantastic!
I might dabble in the code to see if I can try and build it, but I'd rather know what you think of the idea. Are you guys open to suggestions for other alerting methods?

Also, I think there's a market for alerting plugins, just like the datasource plugins: it might be interesting to allow for higher level access to the alerting API and provide plugins to hit anything (IFTT, Twilio, Synology NAS etc.). I don't have much experience in the grafana code, so I don't know how it is done, but there's my suggestion.

[Gui13]

I have a functioning implementation right now, I could do a PR if you are up to it.