Enable pgquery (#1048)

I try to use pgquery, it needs some configuration in .env file.
I think if we use pgquery instead of mapnik, the performace will be good.

.env

@@ -48,3 +48,10 @@ MAX_PARALLEL_PSQL=5
 
 # Number of parallel threads to use when generating vector map tiles
 COPY_CONCURRENCY=10
+
+# Variables for generate tiles using PGquery
+PGHOSTS_LIST=
+# Uncomment when used PGquery
+#EXPORT_DIR=/import
+NO_GZIP=1
+USE_KEY_COLUMN=1