[Misc] support linux for vllm cpu local development

[nurali-techie]

Pull Request Description

• Added kustomization.yaml to use Linux image for aibrix/vllm-cpu-env.
• Renamed config dir to macos.
• README now includes Linux related steps. Mac related steps are moved under the Mac heading.

Action Item

1. We need to push Linux docker image aibrix/vllm-cpu-env:linux-amd64 at https://hub.docker.com/r/aibrix/vllm-cpu-env/tags

Related Issues

Resolves: #866

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[Jeffwan]

@varungup90 I see you help support this case in the slack channel with @nurali-techie . please help review this change