[Metrics] Make context optional for histogram instruments in Metrics SDK

[ThomsonTan]

Fixes #2155

Changes

This PR extracts the context related change in #2341, also the change of making LongCounter and LongHistogram as unsigned type is picked up.

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #2416 (e05d12f) into main (71d0e50) will decrease coverage by 0.35%.
The diff coverage is 56.33%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2416      +/-   ##
==========================================
- Coverage   87.41%   87.06%   -0.35%     
==========================================
  Files         199      199              
  Lines        6052     6079      +27     
==========================================
+ Hits         5290     5292       +2     
- Misses        762      787      +25     

Files	Coverage Δ
api/include/opentelemetry/metrics/noop.h	41.18% <ø> (+3.93%)	⬆️
...i/include/opentelemetry/metrics/sync_instruments.h	100.00% <100.00%> (ø)
...clude/opentelemetry/sdk/metrics/sync_instruments.h	100.00% <ø> (+19.52%)	⬆️
sdk/src/metrics/meter.cc	61.45% <100.00%> (ø)
sdk/src/metrics/sync_instruments.cc	65.84% <53.09%> (-13.05%)	⬇️

... and 1 file with indirect coverage changes

[lalitb]

Thanks for the fix. Nicely done.

[marcalff]

LGTM, thanks for the fix.