[Metrics SDK] Metric aggregation temporality controls

[lalitb]

Fixes #1339

Changes

As preferred aggregation temporality concept is removed from specs, and is made as function of instrument-kind (see section here - https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#metricreader) , following changes are done -

• Modify GetAggregationTemporality() method in MetricReader. The methods now take in instrument type/kind, that lets exporter find which temporality to use based on the instrument.
• Add GetAggregationTemporality() method in MetricExporter. This method takes the instrument type/kind, and returns the correct temporality to use based on the exporter used -
  • OTLP exporter can be configured with a preferred temporality
  • Prometheus only uses cumulative (as it doesn't support delta).

For significant contributions please make sure you have completed the following items:

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

[codecov]

Codecov Report

Merging #1541 (b06345c) into main (124b198) will decrease coverage by 0.04%.
The diff coverage is 57.15%.

@@            Coverage Diff             @@
##             main    #1541      +/-   ##
==========================================
- Coverage   83.96%   83.93%   -0.03%     
==========================================
  Files         156      156              
  Lines        4905     4908       +3     
==========================================
+ Hits         4118     4119       +1     
- Misses        787      789       +2     

Impacted Files	Coverage Δ
...dk/include/opentelemetry/sdk/metrics/instruments.h	0.00% <ø> (ø)
...nclude/opentelemetry/sdk/metrics/metric_exporter.h	100.00% <ø> (ø)
.../include/opentelemetry/sdk/metrics/metric_reader.h	50.00% <ø> (ø)
sdk/src/metrics/state/metric_collector.cc	50.00% <0.00%> (ø)
...metrics/export/periodic_exporting_metric_reader.cc	73.92% <50.00%> (-3.35%)	⬇️
exporters/ostream/src/metric_exporter.cc	92.13% <66.67%> (-1.31%)	⬇️
sdk/src/metrics/metric_reader.cc	59.38% <100.00%> (-4.51%)	⬇️
sdk/src/metrics/state/temporal_metric_storage.cc	93.23% <100.00%> (ø)
ext/src/http/client/curl/http_client_curl.cc	81.44% <0.00%> (+0.38%)	⬆️
sdk/src/trace/batch_span_processor.cc	91.41% <0.00%> (+0.79%)	⬆️

[ThomsonTan]

@lalitb can you please resolve the merging conflict?

[lalitb]

@lalitb can you please resolve the merging conflict?

Fixed. Thanks.