Convert UpDownCounters to Prometheus gauges

[dashpole]

Fixes #3353

Spec: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/data-model.md#sums-1

OpenTelemetry Sums follows this logic:

• If the aggregation temporality is cumulative and the sum is monotonic, it MUST be converted to a Prometheus Counter.
• If the aggregation temporality is cumulative and the sum is non-monotonic, it MUST be converted to a Prometheus Gauge.

[codecov]

Codecov Report

Merging #3358 (483b1a5) into main (6c0a7c4) will increase coverage by 0.0%.
The diff coverage is 100.0%.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #3358   +/-   ##
=====================================
  Coverage   77.8%   77.8%           
=====================================
  Files        164     164           
  Lines      11278   11282    +4     
=====================================
+ Hits        8778    8788   +10     
+ Misses      2303    2297    -6     
  Partials     197     197           

Impacted Files	Coverage Δ
exporters/prometheus/exporter.go	81.8% <100.0%> (+0.4%)	⬆️
exporters/jaeger/jaeger.go	91.1% <0.0%> (+0.8%)	⬆️
sdk/trace/batch_span_processor.go	81.9% <0.0%> (+1.7%)	⬆️