Add bicycle, foot, horse, and mtb_scale to the transportation layer

Resolve https://github.com/openmaptiles/openmaptiles/issues/422
Resolve https://github.com/openmaptiles/openmaptiles/issues/512
Resolve https://github.com/openmaptiles/openmaptiles/issues/602

An extended and refined alternative to https://github.com/openmaptiles/openmaptiles/pull/573

layers/transportation/mapping.yaml

@@ -133,6 +133,22 @@ man_made_field: &man_made
 z_order_field: &z_order
   name: z_order
   type: wayzorder
+bicycle_field: &bicycle
+  key: bicycle
+  name: bicycle
+  type: string
+foot_field: &foot
+  key: foot
+  name: foot
+  type: string
+horse_field: &horse
+  key: horse
+  name: horse
+  type: string
+mtb_scale_field: &mtb_scale
+  key: mtb:scale
+  name: mtb_scale
+  type: string
 
 tables:
 # etldoc: imposm3 -> osm_highway_linestring
@@ -168,6 +184,10 @@ tables:
     - *usage
     - *public_transport
     - *man_made
+    - *bicycle
+    - *foot
+    - *horse
+    - *mtb_scale
     mapping:
       highway:
       - motorway