[CI/Build] Adopt Mergify for auto-labeling PRs

[russellb]

Import initial configuration for Mergify.
This configuration does the following:

• Auto-label PRs that change docs (docs/ directory or any file
  ending in .md) with the documentation label

• Auto-label PRs that change CI/Build related files with the ci/build label.

• Auto-label PRs with the frontend label if they change files under
  vllm/entrypoints.

• Auto-label PRs with kernel if they change files under csrc. I know more
  paths are needed here.

• Auto-label PRs that go into conflict with main and ping the PR
  author to highlight that a conflict exists. Auto-remove this label
  when conflicts are resolved.

This pattern serves as a starting point. I'm sure there are a lot more
desired labeling additions. Please send me requests and I'll add them!

Closes #9192

Signed-off-by: Russell Bryant [email protected]

---

cc @simon-mo

tasks that someone with commit access needs to do:

• Add the Mergify github application to the vllm-project organization and the
  vllm repository. See https://docs.mergify.com/getting-started/

• Create the following labels. The config uses them and I'm not positive if they
  will get automatically created if they don't exist, so might as well just
  create them.

  • needs-rebase
  • ci/build
  • frontend
  • kernel

[github-actions]

👋 Hi! Thank you for contributing to the vLLM project.
Just a reminder: PRs would not trigger full CI run by default. Instead, it would only run fastcheck CI which starts running only a small and essential subset of CI tests to quickly catch errors. You can run other CI tests on top of those by going to your fastcheck build on Buildkite UI (linked in the PR checks section) and unblock them. If you do not have permission to unblock, ping simon-mo or khluu to add you in our Buildkite org.

Once the PR is approved and ready to go, your PR reviewer(s) can run CI to test the changes comprehensively before merging.

To run CI, PR reviewers can do one of these:

• Add ready label to the PR
• Enable auto-merge.

🚀