feat: MySQL2 semantic convention stability migration

[hannahramadan]

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

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

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 database and networking conventions.

This approach was approved for HTTP migration in #1547

[github-actions]

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