chore: Add config for dependabot.

[liangyuanpeng]

Please briefly answer these questions:

• what problem are you trying to solve? (or if there's no problem, what's the motivation for this change?)

Let dependabot work for auto update github-actions to get rid of deprecated github actions.

Also can update it for argo if you accepts the automatic update of cargo dependencies,

  - package-ecosystem: "cargo"
    directory: "/"
    schedule:
      interval: "weekly"
    labels:
      - "dependencies"

• what changes does this pull request make?

• are there any non-obvious implications of these changes? (does it break compatibility with previous versions, etc)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 74.40%. Comparing base (75e51f4) to head (d2229f5). Report is 2 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #697 +/- ## ========================================== + Coverage 74.38% 74.40% +0.02% ========================================== Files 173 173 Lines 25872 25872 Branches 25872 25872 ========================================== + Hits 19244 19250 +6 + Misses 5425 5420 -5 + Partials 1203 1202 -1 ```

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