[Performance] Migrate all synchronous operations into async/await and promises.

[mavyfaby]

As the application grows bigger and receives a lot of requests, synchronous operations may block some of them, causing the server to fail to do its task. As a result, we'll need to use asynchronous operations to prevent blocking the main thread of the application.

If you're interested in contributing, please do fork and read our CONTRIBUTING guide!

CC: @TotalElderBerry @ampats04