feat: add OTLP adapter for OpenTelemetry Protocol support

[seuros]

Summary

• Add generic OTLP adapter that works with any OTLP-compatible backend (SigNoz, Jaeger, Grafana Tempo, Honeycomb, etc.)
• Uses HTTP/JSON transport on port 4318 (/v1/traces)
• Supports exception capture with full OTLP structure (resourceSpans, scopeSpans, spans with exception events)
• Add DRY concerns: StacktraceBuilder, TraceContext

Configuration Helpers

# Generic OTLP
config.use_otlp(endpoint: "http://localhost:4318", service_name: "my-app")

# Service-specific convenience helpers
config.use_signoz(signoz_api_key: ENV['SIGNOZ_API_KEY'])
config.use_jaeger(endpoint: "http://jaeger:4318")
config.use_tempo(endpoint: "http://tempo:4318")

Test plan

• Unit tests for OTLP adapter (12 tests)
• VCR cassettes recorded against live OTEL Collector
• Configuration helpers tested
• Payload structure validation tests