[CI] Update mergify config to automatically approve and merge mergify PRs

[innobead]

What's the CI task to develop? Please describe

As title, this can improve the productivity of approving and merging backport PRs.

Describe the items of the task development (DoD, definition of done) you'd like

Update the mergify config of each supported repos.

example: https://github.com/longhorn/longhorn/blob/master/.github/mergify.yml

Additional context

[innobead]

Assigned to @derekbit , this is related to the productivity of issue and pr management, so can better know how to improve this in general.