docker-compose: Need to tell sheet-sync to allocate ids

NOTE: This is only safe if we're only running one.

Later we should make a way to control this in config so one node has it
but others can run non-allocating sheetsyncs.

docker-compose.jsonnet

@@ -237,6 +237,7 @@
       // Args for the sheetsync
       command: [
         "--backdoor-port", std.toString($.backdoor_port),
+        "--allocate-ids",
         $.db_connect,
         "/etc/wubloader-creds.json",
         $.edit_url,