This PR adds a proxy endpoint that allows the frontend to send OpenTelemetry traces and logs to the backend, which then forwards them to the ADOT Lambda Layer collector.

What's New

OTLP Proxy Endpoint (/docs/_api/v1/o/{signalType})

• Proxies OTLP telemetry from frontend to local ADOT collector at localhost:4318
• Supports traces (/o/t), logs (/o/l), and metrics (/o/m)
• Uses adblocker-friendly URL paths (/o/* instead of /otlp/*)
• ADOT layer handles authentication and forwarding to Elastic MOTLP

Architecture

• OtlpProxyUsecase - Coordinates the proxy flow
• IOtlpGateway / AdotOtlpGateway - Abstracts OTLP forwarding logic
• OtlpProxyOptions - Configurable OTLP endpoint (defaults to ADOT at localhost:4318)
• OtlpSignalType enum - Type-safe signal type handling with generated extensions

Testing

• ApiWebApplicationFactory - Simplified base factory with reusable ServiceReplacementBuilder for test-specific mocks
• OtlpProxyIntegrationTests - Comprehensive tests verifying URL construction, signal types, and error handling
• EuidEnrichmentIntegrationTests - Updated to use new service mocking pattern

Why?

This enables distributed tracing from frontend to backend, linking user interactions (frontend spans) with API calls (backend spans) under a single trace ID, while keeping backend authentication credentials secure.