Store Gitea data (avatars, attachments, etc.) in Garage/S3

Also adds a new garage gateway role, which only allows RPC (inter-node)
traffic to Garage.

environments/production.json

@@ -5,6 +5,17 @@
       "replication_mode": "2",
       "s3_api_root_domain": ".s3.garage.kosmos.org",
       "s3_web_root_domain": ".web.garage.kosmos.org"
+    },
+    "gitea": {
+      "postgresql_host": "pg.kosmos.local:5432",
+      "config": {
+        "storage": {
+          "type": "minio",
+          "endpoint": "localhost:3900",
+          "location": "garage",
+          "use_ssl": "false"
+        }
+      }
     }
   }
-}
+}