refactor: make database volume name service-specific (vikunja-db-data)

docker-compose.yml

@@ -25,7 +25,7 @@ services:
       POSTGRES_USER: vikunja
       POSTGRES_DB: vikunja
     volumes:
-      - db-data:/var/lib/postgresql/data
+      - vikunja-db-data:/var/lib/postgresql/data
     network_mode: service:vikunja-ts
     restart: unless-stopped
 
@@ -50,4 +50,4 @@ services:
     restart: unless-stopped
 
 volumes:
-  db-data:
+  vikunja-db-data: