feat(metrics): multi-instrument async callback support

[legendecas]

Which problem is this PR solving?

Added multi-instrument async callback support.

Fixes #2956

Short description of the changes

• Added ValueType support in async instruments.
• Changes on meter.createObservableCounter, meter.createObservableGauge, meter.createObservableUpDownCounter
  • removed the second parameter callback
  • returns an Observable object on which callbacks can be registered or unregistered.
• Added meter.addBatchObservableCallback and meter.removeBatchObservableCallback.
• One callback associated with a set of instruments are called once for each collection. (spec clarification: Clarify async instrument callback identity opentelemetry-specification#2538)

After the change, observable instruments can be used with like:

const meter = api.metrics.getMeter('test-meter');
// Creating an async instrument, similar to synchronous instruments
const observableCounter = meter.createObservableCounter('observable-counter', {}); 

// Register a single-instrument callback
observableCounter.addCallback(async (observableResult) => {  
  // ... do async stuff
  observableResult.observe(1, { attr: 'value' });
});

// Register a multi-instrument callback
meter.addBatchObservableCallback(async (batchObservableResult) => { 
   // ... do async stuff
  batchObservableResult.observe(observableCounter, 1, { attr: 'value' });

  // This is been dropped since it is not associated with the callback at registration.
  batchObservableResult.observe(otherObservable, 2); 
}, [ observableCounter ]);

Type of change

• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How Has This Been Tested?

• ObservableRegistry
• Meter.createObservableXXX
• MetricCollector.collect integrated tests for batch observable callbacks
• ObservableResult trunc values for ValueType.INT

Checklist:

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

[codecov]

Codecov Report

Merging #2966 (fe1bf62) into main (610808d) will decrease coverage by 2.03%.
The diff coverage is 92.85%.

❗ Current head fe1bf62 differs from pull request most recent head 8e07cea. Consider uploading reports for the commit 8e07cea to get more accurate results

@@            Coverage Diff             @@
##             main    #2966      +/-   ##
==========================================
- Coverage   92.54%   90.51%   -2.04%     
==========================================
  Files         183       68     -115     
  Lines        6025     1876    -4149     
  Branches     1284      400     -884     
==========================================
- Hits         5576     1698    -3878     
+ Misses        449      178     -271     

Impacted Files	Coverage Δ
...ages/opentelemetry-api-metrics/src/types/Metric.ts	100.00% <ø> (ø)
...ackages/opentelemetry-api-metrics/src/NoopMeter.ts	97.22% <92.85%> (+24.49%)	⬆️
...s/opentelemetry-core/src/platform/node/sdk-info.ts	0.00% <0.00%> (-100.00%)	⬇️
...opentelemetry-core/src/platform/node/globalThis.ts	0.00% <0.00%> (-100.00%)	⬇️
...pentelemetry-core/src/platform/node/performance.ts	0.00% <0.00%> (-100.00%)	⬇️
...emetry-api-metrics/src/platform/node/globalThis.ts	0.00% <0.00%> (-100.00%)	⬇️
...lemetry-resources/src/detectors/ProcessDetector.ts	31.81% <0.00%> (-68.19%)	⬇️
...pentelemetry-resources/src/detectors/OSDetector.ts	26.66% <0.00%> (-60.00%)	⬇️
...ntelemetry-resources/src/detectors/HostDetector.ts	23.52% <0.00%> (-52.95%)	⬇️
...perimental/packages/otlp-exporter-base/src/util.ts	79.41% <0.00%> (-17.65%)	⬇️
... and 118 more

[legendecas]

I'm marking this ready to be reviewed to let people drop a comment on the new observable APIs. But I'd still like the spec change open-telemetry/opentelemetry-specification#2538 to land first.

[vmarchaud]

as always i'm not the most familiar with metrics (ajd this is a large PR) but code wise lgtm

[dyladan]

Huge effort thanks so much. I'm going to approve but there are some small things that you can do if you want:

• Add tests for the metrics API package for the changed lines. Looks like they're not included in the coverage
• Documentation on how this feature is used
• In the PR a short description of the design of this feature and if you copied another implementation for it might make it easier for others to review.

[legendecas]

@dyladan thank you for the suggestion! I've added some new docs in the README of sdk-metrics-base and updated the short description in the OP.

[pichlermarc]

Looks good as per my understanding of the spec. 🙂
Thanks for the great work! 🚀

[dyladan]

All my questions are resolved. Up to you if you want to merge or wait for more reviews.

[legendecas]

I'll try to land this by the end of tomorrow to get things rolling. Thank you all for reviewing!