[docker-compose] Address linter and code review feedback #554

- Move DOCKER_TAG before EMAIL_DJANGO_DEFAULT in .env for alphabetical ordering
- Add blank line at end of .env file
- Add fallback to DOCKER_TAG in Makefile to handle unset/empty cases

Author: atif09

.env

@@ -8,6 +8,7 @@ API_DOMAIN=api.openwisp.org
 SSH_PRIVATE_KEY_PATH=/home/openwisp/.ssh/id_ed25519
 SSH_PUBLIC_KEY_PATH=/home/openwisp/.ssh/id_ed25519.pub
 VPN_DOMAIN=openvpn.openwisp.org
+DOCKER_TAG=25.10.0
 EMAIL_DJANGO_DEFAULT=example@example.org
 DB_USER=admin
 DB_PASS=admin
@@ -63,4 +64,3 @@ CELERY_SERVICE_NETWORK_MODE=service:openvpn
 METRIC_COLLECTION=True
 # collectstatic
 COLLECTSTATIC_WHEN_DEPS_CHANGE=true
-DOCKER_TAG=latest

Makefile

@@ -23,7 +23,7 @@ pull:
 				 'openwisp-freeradius' 'openwisp-nginx' 'openwisp-openvpn' 'openwisp-postfix' \
 				 'openwisp-websocket' ; do \
 		docker pull --quiet $(USER)/$${image}:$(TAG); \
-		docker tag  $(USER)/$${image}:$(TAG) openwisp/$${image}:$${DOCKER_TAG}; \
+		docker tag  $(USER)/$${image}:$(TAG) openwisp/$${image}:$${DOCKER_TAG:-latest}; \
 	done
 
 # Build