[CPU] Add action to automatically label CPU related PRs

[fadara01]

Purpose

Add action to automatically label CPU related PRs
This helps us stay on top of changes in CPU Backend, and simulate code ownership for people working on CPU backend but are not maintainers.

Test Plan

N/A

Test Result

N/A

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Essential Elements of an Effective PR Description Checklist

• [Yes] 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 in the Google Doc.

[chatgpt-codex-connector]

Codex usage limits have been reached for code reviews. Please check with the admins of this repo to increase the limits by adding credits.

[gemini-code-assist]

Code Review

This pull request adds a Mergify rule to automatically label CPU-related PRs. The change is well-contained and serves a useful automation purpose. My review includes a suggestion to refine the file-matching pattern to improve its accuracy and avoid potential false positives.

[fadara01]

@mgoin @simon-mo could you have a look?

[bigPYJ1151]

LGTM