Add $OMT_HOST support to make start-postserve (#956)

Resolve https://github.com/openmaptiles/openmaptiles/issues/955

Makefile

@@ -53,6 +53,7 @@ endif
 
 # Set OpenMapTiles host
 OMT_HOST := http://$(firstword $(subst :, ,$(subst tcp://,,$(DOCKER_HOST))) localhost)
+export OMT_HOST
 
 # This defines an easy $(newline) value to act as a "\n". Make sure to keep exactly two empty lines after newline.
 define newline

docker-compose.yml

@@ -83,7 +83,7 @@ services:
 
   postserve:
     image: "openmaptiles/openmaptiles-tools:${TOOLS_VERSION}"
-    command: "postserve openmaptiles.yaml --verbose --port ${PPORT:-8090}"
+    command: "postserve openmaptiles.yaml --verbose --serve=${OMT_HOST:-localhost}:${PPORT:-8090}"
     env_file: .env
     networks:
       - postgres_conn