feat(sdk-metrics-base): distinguish between Sum and Gauge in MetricData

[pichlermarc]

Which problem is this PR solving?

We do not distinguish between Sum and Gauge in MetricData. This complicates development of third-party exporters, which are required to rely on InstrumentType, which due to different Aggregations can be confusing and therefore error-prone.

This PR adds SumDataPoint and GaugeDataPoint as a replacement for SingularDataPoint, and includes isMonotonic in SumDataPoint, and updates exporters in this repo accordingly.

Fixes #3063

Short description of the changes

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• breaks existing metrics exporters due to removal of DataPointType.SINGULAR

How Has This Been Tested?

• Existing tests (adapted)

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[codecov]

Codecov Report

Merging #3079 (ac7d6b5) into main (4ee8fe3) will increase coverage by 0.42%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #3079      +/-   ##
==========================================
+ Coverage   92.66%   93.08%   +0.42%     
==========================================
  Files         173      188      +15     
  Lines        5518     6248     +730     
  Branches     1171     1313     +142     
==========================================
+ Hits         5113     5816     +703     
- Misses        405      432      +27     

Impacted Files	Coverage Δ
...ry-exporter-prometheus/src/PrometheusSerializer.ts	95.16% <100.00%> (+0.03%)	⬆️
...metry-sdk-metrics-base/src/aggregator/LastValue.ts	100.00% <100.00%> (ø)
...entelemetry-sdk-metrics-base/src/aggregator/Sum.ts	100.00% <100.00%> (ø)
...elemetry-sdk-metrics-base/src/export/MetricData.ts	100.00% <100.00%> (ø)
.../packages/otlp-transformer/src/metrics/internal.ts	97.72% <100.00%> (-0.43%)	⬇️
...telemetry-sdk-trace-web/src/StackContextManager.ts	94.28% <0.00%> (ø)
...-instrumentation-fetch/src/enums/AttributeNames.ts	100.00% <0.00%> (ø)
...-sdk-trace-web/src/enums/PerformanceTimingNames.ts	100.00% <0.00%> (ø)
...ry-context-zone-peer-dep/src/ZoneContextManager.ts	85.18% <0.00%> (ø)
...ckages/opentelemetry-sdk-trace-web/karma.worker.js	100.00% <0.00%> (ø)
... and 15 more

[legendecas]

This is a great change! Overall LGTM. Just a few suggestions on testing.