[misc] simplify the naming around waiting for a mongo connection

Co-Authored-By: Eric Mc Sween <eric.mcsween@overleaf.com>
Co-Authored-By: Miguel Serrano <mserranom@gmail.com>
Co-Authored-By: Simon Detheridge <s@sd.ai>

services/chat/app.js

@@ -23,7 +23,8 @@ if (!module.parent) {
       settings.internal != null ? settings.internal.chat : undefined,
       (x1) => x1.host
     ) || 'localhost'
-  mongodb.clientConnecting
+  mongodb
+    .waitForDb()
     .then(() => {
       Server.server.listen(port, host, function (err) {
         if (err) {