[Mergify] Init config

[gcanlin]

PLEASE FILL IN THE PR DESCRIPTION HERE ENSURING ALL CHECKLIST ITEMS (AT THE BOTTOM) HAVE BEEN CONSIDERED.

Purpose

Follow vLLM, Mergify can automatically apply labels to make PRs clearer and more discoverable, especially for hardware platform maintainers to quickly recognize and follow relevant changes.

Test Plan

Test Result

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Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft.

BEFORE SUBMITTING, PLEASE READ https://github.com/vllm-project/vllm-omni/blob/main/CONTRIBUTING.md (anything written below this line will be removed by GitHub Actions)

[gcanlin]

cc @ywang96 @hsliuustc0106 @david6666666 @tjtanaa @faaany

[gcanlin]

After #774 merged, could we consider enable mergify to automatically add label? @hsliuustc0106

[hsliuustc0106]

I think this is worth trying

[gcanlin]

I think this is worth trying

Thanks! Feel free to add more tags condition to categorize modules.