SQL Expressions: Rework backend errors and error instrumentation (#109633)

* Capture error_type label on metrics/traces
* Make error messages more helpful to user
* Use errutil, categorized errors, and tie them to error_type (category in code)
* Misc trace fixes
* Add metric to track SQL input conversion

pkg/expr/ml.go

@@ -130,7 +130,7 @@ func (m *MLNode) Execute(ctx context.Context, now time.Time, _ mathexp.Vars, s *
 	}
 
 	// process the response the same way DSNode does. Use plugin ID as data source type. Semantically, they are the same.
-	responseType, result, err = s.converter.Convert(ctx, mlPluginID, dataFrames, false)
+	responseType, result, err = s.converter.Convert(ctx, mlPluginID, dataFrames)
 	return result, err
 }