examples: add an OTLP example

[inge4pres]

Describe the current state

OTLP support is merged but we don't have an example for it.
While still experimental, we should have a file that showcases how to use OTLP to send telemetry data to a collector.

Describe the desired state

We add an example showing how to use the OTLP exporter.

This may require adding more exports in src/sdk.zig to make the exporter visibile to consumers of the module.