add dummyUsage to certain profiles

If BRouter calculates a route with a cycling or hiking profile,
the `smoothness` tag is included in the response. That enables
a statistical analysis for the calculated route (distribution of
smoothness tags by distance).

See the analysis sidebar at https://brouter.m11n.de/ for an example.

misc/profiles2/fastbike.brf

@@ -260,6 +260,8 @@ assign classifiermask add          isbadoneway
                       add multiply islinktype     8
                           multiply isgoodforcars 16
 
+# include `smoothness=` tags in the response's WayTags for track analysis
+assign dummyUsage = smoothness=
 
 ---context:node  # following code refers to node tags