stack: compose DATABASE_URL from POSTGRES_* vars instead of duplicating in .env

stack/.env

@@ -10,7 +10,6 @@ POSTGRES_PASSWORD=clearview
 
 ADMINER_PORT=8081
 
-DATABASE_URL=postgresql://clearview:clearview@postgres:5432/clearview
 ONBOARDING_CLIENT_ID=
 ONBOARDING_CLIENT_SECRET=
 ONBOARDING_REDIRECT_URI=

stack/docker-compose.yml

@@ -7,7 +7,7 @@ services:
       - "${CLEARVIEW_PORT}:80"
     environment:
       TZ: ${TZ}
-      DATABASE_URL: ${DATABASE_URL}
+      DATABASE_URL: postgresql://${POSTGRES_USER}:${POSTGRES_PASSWORD}@${POSTGRES_HOST}:${POSTGRES_PORT}/${POSTGRES_DB}
       ONBOARDING_CLIENT_ID: ${ONBOARDING_CLIENT_ID}
       ONBOARDING_CLIENT_SECRET: ${ONBOARDING_CLIENT_SECRET}
       ONBOARDING_REDIRECT_URI: ${ONBOARDING_REDIRECT_URI}