This PR solving the speed and memory issue with buildings aggregation on zoom level 13. The problem was to create ST_ClusterDBScan which failed after try to cluster a larger area. Now it will make cluster only in "small" polygon using 'country_osm_grid` which covers the world's lands. This PR solving #1022 and #974
building
Docs
Read the layer documentation at http://openmaptiles.org/schema#building

