fix(exporter/prometheus): export exemplars on native histograms

[tcolgate]

The prometheus exporter had a TODO relating to adding of exemplars to exported native histogram. The upstream prometheus client has been fixed, and otel already depends on the fixed version.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.8%. Comparing base (04859c7) to head (c166e90).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #6953     +/-   ##
=======================================
- Coverage   82.8%   82.8%   -0.1%     
=======================================
  Files        261     261             
  Lines      24312   24313      +1     
=======================================
- Hits       20144   20141      -3     
- Misses      3793    3797      +4     
  Partials     375     375             

Files with missing lines	Coverage Δ
exporters/prometheus/exporter.go	82.3% <100.0%> (+<0.1%)	⬆️

... and 3 files with indirect coverage changes

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[pellared]

otel already depends on the fixed version.

This is not true

[tcolgate]

@dashpole, can you please take a look?

otel already depends on the fixed version.

This is not true.

How so? exporters/prometheus/go.mod already lists 1.22.0, which includes the handling of exemplars on native histograms. Are there bugs? (the test I included passes, and that routes through the relevant code)

[pellared]

which includes the handling of exemplars on native histograms

It does not. See prometheus/client_golang#1816 (comment)

the test I included passes, and that routes through the relevant code

It does not seem to assert everything. See: https://github.com/open-telemetry/opentelemetry-go/pull/6772/files

I think that this PR can should be closed given we already have #6772