[WIP] Suppression of nested logs from dependencies

[lalitb]

Raising this PR as alternate approach to fix #1171, by extending the Context structure to store the suppression flag. The PR is to discuss this approach. The earlier approach #1315 was based on tokio runtime, and generalizing it would have been difficult.

Change summary

1. Move FutureExt and WithContext constructs from trace/context.rs to context.rs.
2. Add suppress_logs flag in Context struct

pub struct Context {
    #[cfg(feature = "trace")]
    pub(super) span: Option<Arc<SynchronizedSpan>>,
    pub suppress_logs: bool,
    entries: HashMap<TypeId, Arc<dyn Any + Sync + Send>, BuildHasherDefault<IdHasher>>,
}

3. Add with_suppression method in Context to enable suppression:

impl Context {
  ...
    pub(super) fn with_suppression(&self) -> Self {
        Context {
            suppress_logs: true,
            entries: self.entries.clone(),
            ..self.clone()
        }
    }
}

4. Add with_current_context_supp method in FutureExt:

pub trait FutureExt: Sized {
    ...
    fn with_current_context_supp(self) -> WithContext<Self> {
        let otel_cx = Context::current().with_suppression();
        self.with_context(otel_cx)
    }
}

5. Suppress in Exporter::export method:

impl LogExporter for OtlpHttpClient {
    async fn export(&mut self, batch: Vec<LogData>) -> LogResult<()> {
        async {
            // export logic
       }
        .with_current_context_supp()
        .await
    }

6. Check if suppression is enabled in LogProcessor:

impl<R: RuntimeChannel<BatchMessage>> LogProcessor for BatchLogProcessor<R> {
    ...
    #[cfg(feature = "logs_level_enabled")]
    fn event_enabled(&self, _level: Severity, _target: &str, _name: &str) -> bool {
        !Context::current().suppress_logs
    }
}

7. How to test:

run opentelemetry-otlp/examples/basic-otlp-http/ example, while collector is running (using docker-compose up).

[lalitb]

As this PR came into discussion in today's community meeting, summarising the challenge with the current solution -

The PR adds the suppress_logs flag in the Context, and the Context object is propagated inside the async task. However, wrapping the future with FutureExt::WithExt will not cascade the wrapping behavior to all internal futures. So if these internal futures (which could be from external (say) Hyper crate) get invoked in a separate thread, they won't see the suppression flag from context. And we can't explicitly apply the wrapper to each async function of third-party crates. This means, that if the logging macro is invoked from inside one of these async tasks, the suppression_flag won't be set and thus the logs are not suppressed.

[lalitb]

closing this PR. The changes would be done based on the options discussed here - https://github.com/open-telemetry/opentelemetry-rust/issues/761#issuecomment-2121548678.