refactor(db): replace connectDb import paths and introduce new connect module

- Updated import paths for connectDb across various files to use the new centralized connect module.
- Removed the old connectDb file to streamline the database connection logic.
- Ensured all tests and models reference the new connection method for consistency.

api/db/index.js

@@ -0,0 +1,8 @@
+const mongoose = require('mongoose');
+const { createModels } = require('@librechat/data-schemas');
+const { connectDb } = require('./connect');
+const indexSync = require('./indexSync');
+
+const models = createModels(mongoose);
+
+module.exports = { connectDb, indexSync, ...models };