Enforce timeouts

[cijothomas]

BatchExportProcessor, PeriodicReader has been rewritten to use own thread. In the new implementation, they do not enforce timeouts and instead relies on Exporters to enforce timeouts.

Tonic currently enforce timeout - default 10, and respects both OTEL_EXPORTER_OTLP_TIMEOUT and the signal specific override of this.
Reqwest-Blocking does not enforce timeout, so the default timeout from Reqwest-Blocking client, which is 30 seconds, is the only one.
Need to fix this to also enforce timeout like the tonic crate.

We also need to document that OTEL_BLRP_EXPORT_TIMEOUT,OTEL_BSP_EXPORT_TIMEOUT, OTEL_METRIC_EXPORT_TIMEOUT are not honored by default in the SDK.

[cijothomas]

#[cfg(not(target_arch = "wasm32"))]
#[async_trait]
impl HttpClient for reqwest::blocking::Client {
async fn send_bytes(&self, request: Request) -> Result<Response, HttpError> {
otel_debug!(name: "ReqwestBlockingClient.Send");
let mut request: reqwest::blocking::Request = request.try_into()?;
let request_timeout = request.timeout_mut();
if request_timeout.is_none() {
request_timeout.replace(std::time::Duration::from_secs(30));
}
let mut response = self.execute(request)?.error_for_status()?;
let headers = std::mem::take(response.headers_mut());
let mut http_response = Response::builder()
.status(response.status())
.body(response.bytes()?)?;
*http_response.headers_mut() = headers;

        Ok(http_response)
    }
}

The above should work for Reqwest::Blocking.

[cijothomas]

Its better to do it in the opentelemetry-otlp exporter rather than in the http crate, as it needs to get the time out vases from otlp specific env variables.

[cijothomas]

Additional fix to be done
BatchProcessor currently has a timeout it is not enforced. It is better to remove it from API.

/// .with_max_export_timeout(Duration::from_secs(30))