Add requires.tables to <layer>.yaml (#1236)

**NOTE** this can only be merged after the next tools version is released.

Added required Postgres tables to the `<layer>.yaml` definition.
Close: #1220

PR of tools: https://github.com/openmaptiles/openmaptiles-tools/pull/370

layers/place/place.yaml

@@ -1,5 +1,10 @@
 layer:
   id: "place"
+  requires:
+    tables:
+      - ne_10m_admin_1_states_provinces
+      - ne_10m_admin_0_countries
+      - ne_10m_admin_1_states_provinces
   description: |
       The place layer consists out of [countries](http://wiki.openstreetmap.org/wiki/Tag:place%3Dcountry),
       [states](http://wiki.openstreetmap.org/wiki/Tag:place%3Dstate) and [cities](http://wiki.openstreetmap.org/wiki/Key:place).