Add comment on why we do not error out when prepare fails.

plugins/inputs/sql/sql.go

@@ -392,6 +392,11 @@ func (s *SQL) Start(_ telegraf.Accumulator) error {
 		stmt, err := s.db.PrepareContext(ctx, q.Query)
 		cancel()
 		if err != nil {
+			// Some database drivers or databases do not support prepare
+			// statements and report an error here. However, we can still
+			// execute unprepared queries for those setups so do not bail-out
+			// here but simply do leave the `statement` with a `nil` value
+			// indicating no prepared statement.
 			s.Log.Warnf("preparing query %q failed: %w; falling back to unprepared query", q.Query, err)
 			continue
 		}