mongoose 6 upgrade and compatibility fix

[angambaLoitongbam]

Description of changes

upgraded to mongoose 6 removed useMongoClient from options in openDatabaseConnection.js fix admin/server/api/list/get.js

Related issues (if any)

Testing

• [ ] List browser version(s) any admin UI changes were tested in:
• [ ] Please confirm you've added (or verified) test coverage for this change.
• [ ] Please confirm npm run test-all ran successfully.