Remove Context from sync instruments

[cijothomas]

Opening a PR which removes Context as part of the parameters to the measurement reporting API for Counter. If this is agreed, I can remove it for other sync instruments as well. (Updated to remove for all sync instruments) I am not sure if this was intentionally kept, as the Metrics API spec removed this long ago(?) or it never existed in the spec. The SDK could infer the current implicit context OR we could introduce a new ctr.AddWithContext() accepting explicit context if there is a need for passing non-implicit context..

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[hdost]

I believe @jtescher added it last year.

[jtescher]

I think the main use here would be for exemplars, but it's not being used yet. Could work that through first and see if we can delete it after that, or I suppose alternatively we could remove it now and re-add it if needed for exemplars.

[lalitb]

It seems the specs lets the language implementation decide whether to pass the Context parameter explicitly, or else use the current active Context. C++ and Java provides overload methods with Context parameter, Rust has this parameter as mandatory, while other languages use the currently active Context.

[cijothomas]

I think the main use here would be for exemplars, but it's not being used yet. Could work that through first and see if we can delete it after that, or I suppose alternatively we could remove it now and re-add it if needed for exemplars.

Would you agree to the following plan:

1. Remove the Context parameter from instruments now. (This PR)
2. When working on Exemplar + the capability to add attributes from Baggage (the only 2 features in Metrics that are spec-ed out which require Context), we can start with relying on the implicit context without requiring user to explicitly pass it.
3. If there is a desire to provide a different context than the implicit one, introduce a new api (counter.AddWithContext()) that accepts the context (like C++, Java)

[lzchen]

Title should be renamed to only address sync counters

[jtescher]

Would you agree to the following plan:

1. Remove the Context parameter from instruments now. (This PR)
2. When working on Exemplar + the capability to add attributes from Baggage (the only 2 features in Metrics that are spec-ed out which require Context), we can start with relying on the implicit context without requiring user to explicitly pass it.
3. If there is a desire to provide a different context than the implicit one, introduce a new api (counter.AddWithContext()) that accepts the context (like C++, Java)

Yeah I think that's fine, we have both options when creating traces, I think long term having both is reasonable.

[codecov]

Codecov Report

Patch coverage: 69.2% and project coverage change: -0.1 ⚠️

Comparison is base (e773f92) 50.7% compared to head (0647224) 50.7%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1076     +/-   ##
=======================================
- Coverage   50.7%   50.7%   -0.1%     
=======================================
  Files        165     165             
  Lines      19808   19808             
=======================================
- Hits       10059   10058      -1     
- Misses      9749    9750      +1     

Impacted Files	Coverage Δ
opentelemetry-api/src/metrics/noop.rs	5.5% <0.0%> (ø)
opentelemetry-prometheus/src/lib.rs	84.5% <ø> (ø)
opentelemetry-sdk/src/lib.rs	100.0% <ø> (ø)
...etry-sdk/src/testing/metrics/in_memory_exporter.rs	0.0% <ø> (ø)
opentelemetry/src/lib.rs	100.0% <ø> (ø)
stress/src/metrics.rs	14.2% <0.0%> (ø)
...entelemetry-api/src/metrics/instruments/counter.rs	30.3% <100.0%> (ø)
...telemetry-api/src/metrics/instruments/histogram.rs	64.5% <100.0%> (ø)
...try-api/src/metrics/instruments/up_down_counter.rs	26.6% <100.0%> (ø)
opentelemetry-sdk/src/metrics/instrument.rs	30.1% <100.0%> (ø)

... and 1 file with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.

[cijothomas]

@jtescher @hdost @lzchen This is rebased from main, and is ready for merge, once approved! Please take a look! @TommyCpp I'd like to ensure this is part of the upcoming release (as metrics already has breaking change, so why not have them all in one go!)