[WIP] Suppress nested traces from instrumented dependencies

[lalitb]

Fixes #1171

Need few changes before making it ready for review.

• The SuppressionGuard struct should be runtime agnostic. As of now, it is using task-local from tokio runtime.
• Need to add suppression logic across traces and logs, and OTLP-gRPC and OTLP-HTTP exporters.
  Future change : As of now, Context uses thread-local storage. It can also optionally support task-local storage as supported by otel-js, otel-dotnet. And then Context can be leveraged for suppression.

Changes

Please provide a brief description of the changes here.

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)

[codecov]

Codecov Report

Attention: 84 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
opentelemetry-sdk/src/trace/mod.rs	100.0% <100.0%> (ø)
opentelemetry-sdk/src/logs/log_processor.rs	0.0% <0.0%> (ø)
opentelemetry-otlp/src/exporter/http/logs.rs	0.0% <0.0%> (ø)
opentelemetry-sdk/src/suppression.rs	0.0% <0.0%> (ø)

... and 27 files with indirect coverage changes

📢 Thoughts on this report? Let us know!.

[jtescher]

hm holding this type of guard across await points does not generally work as expected. You would likely need to do a similar future wrapping strategy that we have in

opentelemetry-rust/opentelemetry/src/trace/context.rs

Lines 375 to 384 in 28d8cf9

	impl<T: std::future::Future> std::future::Future for WithContext<T> {
	type Output = T::Output;
	fn poll(self: Pin<&mut Self>, task_cx: &mut TaskContext<'_>) -> Poll<Self::Output> {
	let this = self.project();
	let _guard = this.otel_cx.clone().attach();
	this.inner.poll(task_cx)
	}
	}

[lalitb]

Thanks for the suggestion @jtescher. I tried the approach you suggested, basically holding the guard within Context, and try to propagate it across async functions. Seems I am still doing something different, as it is not working. Though I will debug if further, just in case you find some issue in the approach, or any other suggestions. I initially thought it would be straightforward and tokio task_local value is propagated automatically through the chain of async method calls, but probably this is not :)

[lalitb]

closing this PR as @shaun-cox and @TommyCpp had alternate suggestion to extend the Context structure to support suppressing nested logs, Will be raising draft PR to further discuss that approach,