Specify metrics provided by platform

[pdudits]

Specification should list any metrics it should emit out-of-the-box, or with simple configuration option.

Candidates would be:

• JVM metrics as specified https://opentelemetry.io/docs/specs/semconv/runtime/jvm-metrics/
• HTTP client and server metrics as specified https://opentelemetry.io/docs/specs/semconv/http/http-metrics

Implementors should respect the requirement levels Semantic conventions document of all stable metrics and their attributes.