Allow custom ports for postserve/tileserver (#887)

* `make start-postserve PPORT=8000`
* `make start-tileserver TPORT=9000`

Note that both ports need to be the same on host and inside the docker container because the services include a URL to the tiles as part of their manifest.

docker-compose.yml

@@ -71,11 +71,11 @@ services:
 
   postserve:
     image: "openmaptiles/openmaptiles-tools:${TOOLS_VERSION}"
-    command: postserve openmaptiles.yaml --verbose
+    command: "postserve openmaptiles.yaml --verbose --port ${PPORT:-8090}"
     env_file: .env
     networks:
       - postgres_conn
     ports:
-      - "8090:8090"
+      - "${PPORT:-8090}:${PPORT:-8090}"
     volumes:
       - .:/tileset