test(otlp): add local HTTP export integration test

[NewYaroslav]

Summary

• Add an OTLP integration test that starts a local SimpleWeb::Server<HTTP> endpoint.
• The test exposes:
  • GET /health for readiness polling.
  • POST /v1/logs for capturing the OTLP payload.
• It configures OtlpHttpLogger to export to the local server and verifies the captured JSON contains expected OTLP fields.

Notes

• The test is guarded by LOGIT_WITH_OTLP; without OTLP it becomes a no-op executable.
• The test avoids requiring a real OpenTelemetry Collector or Loki instance.

Testing

Not run in this environment.