This PR partially addresses open-telemetry/opentelemetry-go-contrib#7246 by introducing support for category-specific values in the OTEL_SEMCONV_STABILITY_OPT_IN environment variable. For example, multiple categories should be supported without error:

export OTEL_SEMCONV_STABILITY_OPT_IN=http,database,messaging/dup

Changes

Please provide a brief description of the changes here.

Note: if the PR is touching an area that is not listed in the existing areas, or the area does not have sufficient domain experts coverage, the PR might be tagged as experts needed and move slowly until experts are identified.

Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• schema-next.yaml updated with changes to existing conventions.