Add unit suffixes to prometheus metric names

[dashpole]

Fixes #3288

This adds a new option, WithoutUnits() that disables this behavior for all metrics, and maintains the status quo.

I've opted to only rename units we explicitly support in our units package, rather than a more complete set like the collector does. I've also opted not to try and convert milliseconds to seconds, as the conversion (dividing by 1000) won't be straightforward with exponential histograms.

Open Question: Is 1 only applicable to ratios and fractions, or does it apply to any unitless metric? I was told that it only applies to ratios and fractions in the collector version of this. The spec says:

Instruments for utilization metrics (that measure the fraction out of a total) are dimensionless and SHOULD use the default unit 1 (the unity).
Instruments that measure an integer count of something SHOULD only use annotations with curly braces to give additional meaning without the leading default unit (1). For example, use {packets}, {errors}, {faults}, etc.

But I can't tell if there are metrics which don't fall into either category and can use 1 without being a ratio.

[codecov]

Codecov Report

Merging #3352 (a7c8fee) into main (1d9d4b2) will decrease coverage by 0.0%.
The diff coverage is 80.7%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #3352     +/-   ##
=======================================
- Coverage   77.9%   77.9%   -0.1%     
=======================================
  Files        164     164             
  Lines      11348   11363     +15     
=======================================
+ Hits        8850    8861     +11     
- Misses      2301    2305      +4     
  Partials     197     197             

Impacted Files	Coverage Δ
exporters/prometheus/exporter.go	84.0% <76.1%> (+0.7%)	⬆️
exporters/prometheus/config.go	100.0% <100.0%> (ø)
sdk/trace/batch_span_processor.go	81.1% <0.0%> (-0.9%)	⬇️
exporters/jaeger/jaeger.go	90.3% <0.0%> (-0.9%)	⬇️

[ttys3]

using _ratio is really bad if you use an promethus exporter

requests_total will become: requests_ratio_total Omz