[ci] Make building wheels per commit optional

[khluu]

• We don't need per commit wheels all the time. If anyone needs a commit wheel, unblocking it takes like 8-10 mins for CUDA 12.1 wheel to be built.

[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 consists a small and essential subset of CI tests to quickly catch errors. You can run other CI tests on top of default ones by unblocking the steps in your fast-check build on Buildkite UI.

Once the PR is approved and ready to go, please make sure to run full CI as it is required to merge (or just use auto-merge).

To run full CI, you can do one of these:

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

🚀

[khluu]

Test build shows building wheel is blocked now: https://buildkite.com/vllm/release/builds/613

[simon-mo]

We actually documented per commit wheel. Can we just always run 12.1 but not build 11

[khluu]

We actually documented per commit wheel. Can we just always run 12.1 but not build 11

done. 11.8 is optional to build now