Set IsMonotonic to true for opencensus sum

[ktong]

fix #3388

[dashpole]

You will need to update a few unit tests:

• opentelemetry-go/bridge/opencensus/internal/ocmetric/metric_test.go

  Line 314 in ccbc38e

  Data: metricdata.Sum[int64]{

• opentelemetry-go/bridge/opencensus/internal/ocmetric/metric_test.go

  Line 344 in ccbc38e

  Data: metricdata.Sum[float64]{

• opentelemetry-go/bridge/opencensus/internal/ocmetric/metric_test.go

  Line 412 in ccbc38e

  Data: metricdata.Sum[float64]{

And please add an entry in CHANGELOG.md under the Fixed heading

[codecov]

Codecov Report

Merging #3389 (0753059) into main (667a201) will decrease coverage by 0.0%.
The diff coverage is 100.0%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #3389     +/-   ##
=======================================
- Coverage   77.9%   77.9%   -0.1%     
=======================================
  Files        164     164             
  Lines      11359   11359             
=======================================
- Hits        8859    8857      -2     
- Misses      2301    2303      +2     
  Partials     199     199             

Impacted Files	Coverage Δ
bridge/opencensus/internal/ocmetric/metric.go	93.8% <100.0%> (ø)
sdk/trace/batch_span_processor.go	81.1% <0.0%> (-0.9%)	⬇️