Emit a Postgres style JSON plan via `db.query.plan`

[adriangb]

Is your feature request related to a problem or challenge?

This is something we do internally with our tracing / instrumentation and it is super helpful: there's lots of tools for visualizing this plan format, including DataDog (I think).

Describe the solution you'd like

No response

Describe alternatives you've considered

No response

Additional context

No response

[geoffreyclaude]

@adriangb I'm not sure I fully understand: do you want to tag the root span with the JSON plan?
Would you mind sharing an example of what you do internally so its clearer?