Separate docker-compose.yml to test db migration

I think it's not that relevant to our new contributors to install the
db-migration-worker.

docker-compose.db-migration.yml

@@ -0,0 +1,29 @@
+version: "3.7"
+
+services:
+  neo4j:
+    volumes:
+      - mongo-export:/mongo-export
+    environment:
+      - NEO4J_apoc_import_file_enabled=true
+  db-migration-worker:
+    build:
+      context: db-migration-worker
+    volumes:
+      - mongo-export:/mongo-export
+      - ./db-migration-worker/.ssh/:/root/.ssh/
+    networks:
+      - hc-network
+    depends_on:
+      - backend
+    environment:
+      - NEO4J_URI=bolt://neo4j:7687
+      - "SSH_USERNAME=${SSH_USERNAME}"
+      - "SSH_HOST=${SSH_HOST}"
+      - "MONGODB_USERNAME=${MONGODB_USERNAME}"
+      - "MONGODB_PASSWORD=${MONGODB_PASSWORD}"
+      - "MONGODB_AUTH_DB=${MONGODB_AUTH_DB}"
+      - "MONGODB_DATABASE=${MONGODB_DATABASE}"
+
+volumes:
+  mongo-export:

docker-compose.override.yml

@@ -11,33 +11,6 @@ services:
       - /nitro-backend/node_modules
     command: yarn run dev
   neo4j:
-    volumes:
-      - mongo-export:/mongo-export
-      - ./neo4j/import:/var/lib/neo4j/import
     ports:
       - 7687:7687
       - 7474:7474
-    environment:
-      - NEO4J_apoc_import_file_enabled=true
-  db-migration-worker:
-    build:
-      context: db-migration-worker
-    volumes:
-      - mongo-export:/mongo-export
-      - ./db-migration-worker/.ssh/:/root/.ssh/
-    networks:
-      - hc-network
-    depends_on:
-      - backend
-    environment:
-      - NEO4J_URI=bolt://neo4j:7687
-      - "SSH_USERNAME=${SSH_USERNAME}"
-      - "SSH_HOST=${SSH_HOST}"
-      - "MONGODB_USERNAME=${MONGODB_USERNAME}"
-      - "MONGODB_PASSWORD=${MONGODB_PASSWORD}"
-      - "MONGODB_AUTH_DB=${MONGODB_AUTH_DB}"
-      - "MONGODB_DATABASE=${MONGODB_DATABASE}"
-    command: "--smallfiles --logpath=/dev/null"
-
-volumes:
-  mongo-export: