Shift phoenix tracing away from the framework

Phoenix trace export should live in the otel collector configuration rather than being part of the evaluation framework.

Ability to export Phoenix traces via EDOT collector has been demonstrated through the use of [otlphttp exporter](https://github.com/open-telemetry/opentelemetry-collector/tree/main/exporter/otlphttpexporter) and can be used here.

Acceptance Criteria:
- Remove all Phoenix tracing related code from the `src/elastic-evals`
- Add otel-collector-config.yml to Phoenix examples, with instructions how to run EDOT collector that replaces code-based trace export to Phoenix.