Use environment file, but allow it to be changed via an environment variable

docker-compose.yml

@@ -9,6 +9,8 @@ services:
       - POSTGRES_USER=${TTRSS_DB_USER}
       - POSTGRES_PASSWORD=${TTRSS_DB_PASS}
       - POSTGRES_DB=${TTRSS_DB_NAME}
+    env_file:
+      - ${ENV_FILE:-.env}
     volumes:
       - db:/var/lib/postgresql/data
 
@@ -17,6 +19,8 @@ services:
       context:
         ./app
     restart: unless-stopped
+    env_file:
+      - ${ENV_FILE:-.env}
     volumes:
       - app:/var/www/html
       - ./config.d:/opt/tt-rss/config.d:ro
@@ -28,6 +32,8 @@ services:
       context:
         ./app
     restart: unless-stopped
+    env_file:
+      - ${ENV_FILE:-.env}
     volumes:
       - backups:/backups
       - app:/var/www/html
@@ -40,6 +46,8 @@ services:
       context:
         ./app
     restart: unless-stopped
+    env_file:
+      - ${ENV_FILE:-.env}
     volumes:
       - app:/var/www/html
       - ./config.d:/opt/tt-rss/config.d:ro
@@ -52,6 +60,8 @@ services:
     restart: unless-stopped
     ports:
       - ${HTTP_PORT}:80
+    env_file:
+      - ${ENV_FILE:-.env}
     volumes:
       - app:/var/www/html:ro
     depends_on: