New metrics SDK

[jtescher]

This patch updates the metrics SDK to the latest spec. The following breaking changes are introduced.

Metrics API changes:

• Move AttributeSet to SDK as it's not mentioned in the spec or used in the api
• Consolidate AsyncCounter, AsyncUpDownCounter, and AsyncGauge into AsyncInstrument trait and add downcasting for observer callbacks.
• Add AsyncInstrumentBuilder to allow per-instrument callback configuration.
• Allow metric name and description fields to be Cow<'static, str>
• Warn on metric misconfiguration when using instrument builder init rather than returning error
• Update Meter::register_callback to take a list of async instruments and validate they are registered in the callback through the associated Observer
• Allow registered callbacks to be unregistered.

Metrics SDK changes:

• Introduce Scope as type alias for InstrumentationLibrary
• Update Aggregation to match aggregation spec
• Refactor BasicController to spec compliant ManualReader
• Refactor PushController to spec compliant PeriodicReader
• Update metric data fields to match spec, including exemplars.
• Split MetricsExporter into Readers and PushMetricExporters
• Add View implementation
• Remove AtomicNumbers
• Refactor Processors into Pipeline

Metrics exporter changes:

• Update otlp exporter to match new metrics data
• Update otlp exporter configuration to allow aggregation and temporality selectors to be optional.
• Update prometheus exporter to match new metrics data

Example changes:

• Update otlp metrics and prometheus examples.
• Remove basic example as we should be focusing on the OTLP variants

Given the size of the changes I would have preferred to land them individually, but as they all rely on each other it was not practical.

Resolves #897

[hdost]

Great work overall! Don't see any blockers, and I think anything that we missed on this go we can iterate on 😄

[TommyCpp]

Sorry was little busy recently. I will finish reviewing this weekend if that's OK. Or we can merge this and address any issue in the followup PR. Overall great work 🎉

[hdost]

Sorry was little busy recently. I will finish reviewing this weekend if that's OK. Or we can merge this and address any issue in the followup PR. Overall great work tada

I guess I thought we were waiting until after 0.19.0 to merge this? Or are we just not releasing 0.19.0 😅

[TommyCpp]

Sorry was little busy recently. I will finish reviewing this weekend if that's OK. Or we can merge this and address any issue in the followup PR. Overall great work tada

I guess I thought we were waiting until after 0.19.0 to merge this? Or are we just not releasing 0.19.0 😅

Haha yeah, we want to after 0.19. I was worried I will block others from merging the release PR and then this PR. I will #1002 today

[TommyCpp]

Mostly nits and can be addressed in follow-up PRs

[codecov]

Codecov Report

Patch coverage: 39.1% and project coverage change: -12.8 ⚠️

Comparison is base (879d6ff) 69.9% compared to head (0ea2e6d) 57.2%.

Additional details and impacted files

@@           Coverage Diff            @@
##            main   #1000      +/-   ##
========================================
- Coverage   69.9%   57.2%   -12.8%     
========================================
  Files        116     143      +27     
  Lines       9027   17461    +8434     
========================================
+ Hits        6316    9999    +3683     
- Misses      2711    7462    +4751     

Impacted Files	Coverage Δ
opentelemetry-api/src/lib.rs	100.0% <ø> (ø)
...entelemetry-api/src/metrics/instruments/counter.rs	30.3% <0.0%> (-19.7%)	⬇️
opentelemetry-api/src/metrics/instruments/gauge.rs	0.0% <0.0%> (-42.9%)	⬇️
...try-api/src/metrics/instruments/up_down_counter.rs	27.7% <0.0%> (-6.9%)	⬇️
opentelemetry-api/src/metrics/mod.rs	7.0% <0.0%> (-4.4%)	⬇️
opentelemetry-api/src/metrics/noop.rs	5.6% <0.0%> (-28.7%)	⬇️
opentelemetry-otlp/src/lib.rs	29.7% <ø> (ø)
opentelemetry-otlp/src/metric.rs	0.0% <0.0%> (ø)
opentelemetry-otlp/src/span.rs	34.9% <ø> (+34.9%)	⬆️
opentelemetry-otlp/src/transform/metrics.rs	0.0% <0.0%> (ø)
... and 29 more

... and 104 files with indirect coverage changes

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[jtescher]

@TommyCpp any other comments or we good to merge?

[TommyCpp]

@TommyCpp any other comments or we good to merge?

Nope good to merge. Great work!