User-Events log exporter - re-implement Enabled() method to avoid contention

[cijothomas]

Based on stress tests, the Enabled check is a cause for contention.
https://github.com/open-telemetry/opentelemetry-rust-contrib/blob/main/opentelemetry-user-events-logs/src/logs/exporter.rs#L160

Opening an issue to fix this.
We can try if a background thread can periodically check the enabled/disable, and update a AtomicBool, which then can be checked in the hot path.