Prototype for Semantic Conventions for Database Metrics

[maryliag]

Prototype implementation for Semantic Conventions for Database Metrics.

Required for stabilization of semantic convention.

This first prototype will be implemented using Postgres.

Metrics:

• db.client.operation.duration: feat(instrumentation-pg): implementation of metric operation duration #2380
• db.client.connection.count: feat(instrumentation-pg): initial implementation of DB metrics #2349
• db.client.connection.idle.max
• db.client.connection.idle.min
• db.client.connection.max
• db.client.connection.pending_requests: feat(instrumentation-pg): initial implementation of DB metrics #2349
• db.client.connection.timeouts
• db.client.connection.create_time
• db.client.connection.wait_time
• db.client.connection.use_time