Proposal: Enable automerge for devDependencies

## Dev Infrastructure Proposal

I hereby propose that we enable [auto merge](https://dependabot.com/blog/automatic-pull-request-merging/) on `devDependencies` of package.json. The reason why enabling `automerge` is that

1. Save maintainers' time on checking CI and clicking merge
2. Restriction only dev dependencies since typically if won't impact our end users as much as dependencies.

The automerge should comes from high CI coverage fidelity, as some of repositories are not with that high test coverage, we can start automerge from the most covered repositories and then extend to other repos.

Gang, I am looking forward to your opinions.