Add feral-otel4s integration

[armanbilge]

OTel defines some semantic conventions for FaaS "function-as-a-service". A feral-otel4s integration module might be a good place for helpers to live.

• https://opentelemetry.io/docs/reference/specification/metrics/semantic_conventions/faas-metrics/
• https://opentelemetry.io/docs/reference/specification/trace/semantic_conventions/faas/