[Doc][CI/Build] Update docs and tests to use vllm serve

[DarkLight1337]

Follow-up to #5090. As a sanity check, I have also updated the entrypoints tests to use the new CLI.

After this, we can update the Docker images and performance benchmarks to use the new CLI.

cc @EthanqX

[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 trigger fastcheck CI to run, which consists only a small and essential subset of tests to quickly catch errors with the flexibility to run extra individual tests on top (you can do this by unblocking test steps in the Buildkite run).

Full CI run is still required to merge this PR so once the PR is ready to go, please make sure to run it. If you need all test signals in between PR commits, you can trigger full CI as well.

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

• Comment /ready on the PR
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🚀

[simon-mo]

I want to hold this off until the release. So people visiting the nightly docs can directly use the CLI

[simon-mo]

In the meantime, please feel free to start improving it!!!

[mgoin]

Does --model still work or will it cause issues with vllm serve? I'm curious if it is sufficient to replace python -m vllm.entrypoints.openai.api_server with vllm serve or if it specifically replaces python -m vllm.entrypoints.openai.api_server --model

[DarkLight1337]

Does --model still work or will it cause issues with vllm serve?

model_tag is a required positional arg in vllm serve so you have to pass it like vllm serve <model_tag>, regardless of whether --model is passed. The value passed to model is actually overwritten by model_tag (we should not allow both to be passed at the same time tbh).

[mgoin]

Thanks for the clarity, this is a nice PR to update usage LGTM!

[DarkLight1337]

@simon-mo since v0.5.2 has been released, can we merge this?