Collect gauge events

[caruccio]

Hey. Does it makes any sense for you?

[rosskukulinski]

@caruccio Thanks for submitting this! @timothysc do you have a few minutes to take a look?

On first glance, I don't think Gauge is the appropriate metric. I think a better metric would of type Counter, that we increment for every event. This will allow Prometheus to calculate the total events ever as well as the rate of new events for any given time period.

[timothysc]

/lgtm
/approve

[johnSchnake]

@caruccio Could you sign your commits? If you can do that (and ideally rebase onto master) I can merge. I can always merge master into your branch via the UI but would prefer the commits just be your own unless you find it easier to have me do that part.