Assess which micrometer metrics `Counter`s can be converted to `FunctionCounter`s

[DomGarguilo]

If these are monotonically increasing counters, then it would be better to use a FunctionCounter instead of a Gauge. Not sure if they are, need to investigate. The micrometer code to instrument caches uses FunctionCounter internally

Originally posted by @keith-turner in #4518 (comment)

We should look at the places we are using a Counter and determine if it is a good idea to convert them to FunctionCounter.