Implement min/max for the expo-histogram

[jmacd]

Description: The OTLP v0.18 protocol added min/max fields. This code was last written to v0.16 which lacked the necessary fields to complete this.

Testing: Existing test coverage was extended.

[codecov-commenter]

Codecov Report

Merging #215 (e3a09ed) into main (e1ddd9c) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #215      +/-   ##
==========================================
+ Coverage   94.33%   94.35%   +0.02%     
==========================================
  Files          62       62              
  Lines        3263     3297      +34     
==========================================
+ Hits         3078     3111      +33     
- Misses        141      142       +1     
  Partials       44       44              

Impacted Files	Coverage Δ
...p/sdk/metric/aggregator/aggregation/aggregation.go	95.12% <ø> (ø)
...tep/sdk/metric/aggregator/histogram/exponential.go	95.85% <100.00%> (+0.29%)	⬆️
...tstep/sdk/metric/aggregator/histogram/histogram.go	98.16% <100.00%> (+0.14%)	⬆️
.../exporters/otlp/internal/metrictransform/metric.go	97.01% <100.00%> (+0.13%)	⬆️
...etric/exporters/otlp/internal/otlptest/otlptest.go	97.70% <100.00%> (+0.07%)	⬆️
examples/metrics/metrics.go	84.05% <0.00%> (-1.45%)	⬇️

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