Add mongo service to docker-compose.yml for admin transaction storage

.gitignore

@@ -12,3 +12,4 @@ app/tests/coverage/
 *.sublime-project
 dist/
 .worktrees/
+scratch/

docker-compose.yml

@@ -14,6 +14,7 @@ services:
       - "7003:3003"
     depends_on:
       - redis
+      - mongo
     volumes:
       # Named volume, not a host bind-mount: a bind-mounted host directory
       # keeps the host's ownership (usually root), which the container's
@@ -27,6 +28,13 @@ services:
     volumes:
       - redis-data:/data
 
+  mongo:
+    image: mongo:7
+    restart: unless-stopped
+    volumes:
+      - mongo-data:/data/db
+
 volumes:
   redis-data:
   app-log:
+  mongo-data: