Add Waltz metrics documentation to wiki

[whynick1]

We should agree and document on naming convention of metrics before proceeding further.

I think using a class name as a part of a metric name is expressively long and not so useful for monitoring. I'd rather have names like "waltz-server" and "waltz-storage" as top level names. We can map these to domain names in JMX. The second level may be "partition-<partitionId>", which may be mapped to a type name in JMX. I am not sure if it is useful to add metric type name ("counter", "meter", "gauge") at the end of the metric name.

So, my preference is something like "waltz-server.partition-1.high-water-mark". It appears in console like this:

·waltz-server
        ·partition-1
                ·high-water-mark