[Feature] Native OpenTelemetry (OTLP) trace export support to Azure Application Gateway for Containers

**Is your feature request related to a problem? Please describe.**

AGC currently lacks support for emitting distributed tracing data using the OpenTelemetry protocol (OTLP). While it adds a proprietary `trackingId` property in the access log, it does not propagate W3C Trace Context headers (`traceparent`, `tracestate`) or export trace spans. This limits visibility into request flows and breaks trace continuity through the gateway layer.

**Describe the solution you'd like**

- Native support for W3C Trace Context header propagation (`traceparent`, `tracestate`)
- Ability to emit OpenTelemetry spans for inbound HTTP requests
- Configurable OTLP trace export endpoint to an OpenTelemetry Collector which runs within the cluster

**Describe alternatives you've considered**

- Generating synthetic spans from AGC logs (approximate and lossy)
- Correlating logs and traces via `trackingId` (not trace-native)
- Manually injecting synthetic `traceparent` headers (non-native, error-prone)