feat: rest-client HTTP semantic convention stability migration

[hannahramadan]

This PR is intended to assist in the transition from the old to new HTTP semantic conventions. Per the HTTP semantic convention stability migration spec, users should be able to set the environment variable OTEL_SEMCONV_STABILITY_OPT_IN to:

• http to emit stable conventions only
• http/dup to emit both old and the stable conventions
• a blank env var will emit old conventions only

• Span names have also changed. Spans will now be named based on only their method. For example, what used to be HTTP GET is now just GET - spec

The agent is required to maintain this bridge for 6 months and may drop the environment variable in the next major version and emit only the stable HTTP and networking conventions.

This approach was approved in #1547