Enable auto-merge on minor updates.

[Jaehwa-Noh]

What I have done and why

Reference by automerge documentation. https://docs.renovatebot.com/configuration-options/#automerge

  "packageRules": [
    {
      "matchUpdateTypes": ["minor", "patch", "pin", "digest"],
      "automerge": true
    }
  ]
}

Fix #1782

Try to grouping only minor and patch bump up to use an automerge. https://docs.renovatebot.com/presets-group/#groupallnonmajor

[SimonMarquis]

We are already inheriting this configuration that should be equivalent

https://github.com/android/.github/blob/c9c3767d8e4fee5cf3b968c5d4e970ee33973824/renovate-config.json#L8

The main issue is, I think, that we currently only have a global group applied "group:all", which prevents individual PRs to be created and merged separately.

[Jaehwa-Noh]

@SimonMarquis I've checked it, and getting you're right. This project using automerge preset. I think may we grouping only minor update be use.

I'll edit this PR to do that.