Job metrics using meters for values that only ever go up, should we use a counter instead

[adam-fowler]

We are using meters for values that only ever go up eg completed, discarded. These values only ever go up, should we be using the equivalent counter instead

The only status' that go down as well as up seem to be queued and processing

[thoven87]

We are using meters for values that only ever go up eg completed, discarded. These values only ever go up, should we be using the equivalent counter instead

The only status' that go down as well as up seem to be queued and processing

Since meters are not commonly user for metrics that can only go up, it makes sense to use counters instead.

[adam-fowler]

done in #50