Specify configuration mechanism for native instrumentations

[estolfo]

Having Open Telemetry instrumentation natively in libraries has the advantage of keeping ownership of the instrumentation with the library authors; it's a more sustainable way of maintaining instrumentations and is preferable to auto-instrumentations contributed to the language OTel projects.
With that said, there is no specified mechanism for defining and reading configuration for native instrumentations. This issue is meant to propose writing one.

As we discussed in the Specification SIG on 23 May, this may be a discussion for the Configuration SIG and we'd like to pull in opinions from language groups on current conventions.
For example, environment variables are used in Ruby OTel native instrumentations with the formats:
OTEL_RUBY_INSTRUMENTATION_${name}_ENABLED
OTEL_RUBY_INSTRUMENTATION_${name}_CONFIG_OPTS