[C++] Add rows scanned to open telemetry / profiling

[asfimport]

It's not described at https://duckdb.org/dev/profiling but this is included in DuckDB's profiling and was helpful in looking at their scans to see the benefits of predicate push down

Reporter: Jonathan Keane / @jonkeane

Related issues:

• [C++] Add OT spans for the scanner (is blocked by)

_{Note: This issue was originally created as ARROW-15529. Please see the migration documentation for further details.}

[asfimport]

Todd Farmer / @toddfarmer:
This issue was last updated over 90 days ago, which may be an indication it is no longer being actively worked. To better reflect the current state, the issue is being unassigned. Please feel free to re-take assignment of the issue if it is being actively worked, or if you plan to start that work soon.