Enhance the doc only change detection logic to skip the pipeline

[hl475]

Summary

Previously, we skip if every changed file is docs/**, this PR enhances the logic to skip pipeline if every changed file is docs/** OR **/*.md OR mkdocs.yaml

Test

Test on PR with changes on both docs and others

vllm-project/vllm#25116
=>
https://buildkite.com/vllm/ci/builds/35549/steps/canvas

Test on PR with changes on docs only

vllm-project/vllm#25367
=>
https://buildkite.com/vllm/ci/builds/35550/steps/canvas

Test on PR with no changes on docs

vllm-project/vllm#27113
=>
https://buildkite.com/vllm/ci/builds/35547/steps/canvas

Test on merged PR with changes on both docs and others

vllm-project/vllm@f574383
=>
https://buildkite.com/vllm/ci/builds/35546/steps/canvas

Test on merged PR with changes on docs only

vllm-project/vllm@e6e898f
=>
https://buildkite.com/vllm/ci/builds/35545/steps/canvas

Test on merged PR with no changes on docs

vllm-project/vllm@87efc68
=>
https://buildkite.com/vllm/ci/builds/35544/steps/canvas

[khluu]

Thank you!