feat: draft - MySQL2 Semantic Stability

[hannahramadan]

Database semantic convention stability migration spec.

New environment variable OTEL_SEMCONV_STABILITY_OPT_IN:

• 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.

Changes:

• db.system -> db.system.name
• net.peer.name -> server.address
• net.peer.port -> server.port (now an integer, only if present)
• db.name -> db.namespace
• db.statement -> db.query.text
• db.operation → db.operation.name

Removed:

• peer.service

Added:

• error.type
• server.port