Migration of deprecated `bors-ng`

[Taowyoo]

Problem

According to https://bors.tech/newsletter/2023/05/01/tmib-76/ :

As the primary maintainer, I officially declare Bors-NG to be feature frozen and deprecated. The public instance will remain running for awhile, but it will eventually start emitting warnings and be taken down. The source code will always be available if you want to run your own instance.

Solutions

From the article above, it recommend two options:

1. Setup our own instance ng-bors server.
2. Use GitHub's built-in merge queue

We need to make a decision on this.

[Taowyoo]

Done