Prometheus exporter (with configurable port number) for computers running, largest tick times etc

On a semi-related note, it would be useful to track the number of various operations performed by computers. Some ideas:

• Invocations to peripheral.call.
• Invocations to "expensive" fs methods (so fs.open and fs.copy are tracked, but fs.combine, fs.isDir are ignored).

I'm not entirely sure how we'll display it, as they won't all fit on a screen - possibly stick with default timings for now, and add an additional argument to track dump. Something like: [tasks|total|average|max|fs|peripheral].

well, if you add a prometheus exporter you can export absolutely everything you like, in as much detail as you want, and i'll find a way to graph it :)

additionally, monitor updates, peripheral count, turtle count + turtle movement invocations, running computer count, task count, tick times (perhaps as a histogram?)

Closing in favour of #25, because it then means the average time an issue is open is smaller :P.