Implement `OTEL_SEMCONV_STABILITY_OPT_IN` within HTTP-related instrumentation

[kaylareopelle]

Follow the guidelines listed in Semantic Conventions or HTTP to implement the OTEL_SEMCONV_STABILITY_OPT_IN environment variable. This is a requirement before stable HTTP semantic conventions can be added to instrumentation.

Warning Existing HTTP instrumentations that are using v1.20.0 of this document (or prior):

• SHOULD NOT change the version of the HTTP or networking conventions that they emit until the HTTP semantic conventions are marked stable (HTTP stabilization will include stabilization of a core set of networking conventions which are also used in HTTP instrumentations). Conventions include, but are not limited to, attributes, metric and span names, and unit of measure.
• SHOULD introduce an environment variable OTEL_SEMCONV_STABILITY_OPT_IN in the existing major version which is a comma-separated list of values. The only values defined so far are:
  • http - emit the new, stable HTTP and networking conventions, and stop emitting the old experimental HTTP and networking conventions that the instrumentation emitted previously.
  • http/dup - emit both the old and the stable HTTP and networking conventions, allowing for a seamless transition.
  • The default behavior (in the absence of one of these values) is to continue emitting whatever version of the old experimental HTTP and networking conventions the instrumentation was emitting previously.
  • Note: http/dup has higher precedence than http in case both values are present
• SHOULD maintain (security patching at a minimum) the existing major version for at least six months after it starts emitting both sets of conventions.
• SHOULD drop the environment variable in the next major version.

[kaylareopelle]

This relates to #1013

[hannahramadan]

I'd love to work on this issue!

[kaylareopelle]

Great! I've assigned this to you, @hannahramadan

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