Prometheus exporter: do not append _total if the metric already ends in _total

[dashpole]

Fixes #4371

It accomplishes this by trimming _total suffix from counter metrics if we are going to re-add the suffix later.

[codecov]

Codecov Report

Merging #4373 (cea96be) into main (9452b93) will decrease coverage by 0.2%.
The diff coverage is 91.3%.

❗ Current head cea96be differs from pull request most recent head 12554e4. Consider uploading reports for the commit 12554e4 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #4373     +/-   ##
=======================================
- Coverage   83.5%   83.4%   -0.2%     
=======================================
  Files        229     184     -45     
  Lines      18647   14389   -4258     
=======================================
- Hits       15578   12004   -3574     
+ Misses      2751    2157    -594     
+ Partials     318     228     -90     

Files Changed	Coverage Δ
exporters/prometheus/exporter.go	83.1% <91.3%> (+0.3%)	⬆️

... and 67 files with indirect coverage changes

[pellared]

Only the changelog needs to be refined 😉

[MrAlias]

@dashpole this looks ready to merge. Can you resolve the conflicts and sync with main?

[dashpole]

@MrAlias rebased