feat(checkbox-group): support label-key and value-key prop and export checked for default slot

[chouchouji]

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• [ ] Fix linting errors
• [ ] Tests have been added / updated (or snapshots)

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Codecov Report

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

Project coverage is 92.76%. Comparing base (0dbc67c) to head (9b68e5f). Report is 12 commits behind head on dev.

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```diff @@ Coverage Diff @@ ## dev #1640 +/- ## ======================================= Coverage 92.76% 92.76% ======================================= Files 307 307 Lines 7204 7205 +1 Branches 1795 1796 +1 ======================================= + Hits 6683 6684 +1 Misses 454 454 Partials 67 67 ```

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[chouchouji]

@haoziqaq 耗子哥，支持label-key和value-key的话，类型这里label和value也不是必填的了