[Misc] Manage HTTP connections in one place

[DarkLight1337]

This PR adds vllm.connections.HTTP_CONNECTION so that we can reuse the same sync/async client session. It also encapsulates the boilerplate code for common uses of requests and aiohttp libraries.

[github-actions]

👋 Hi! Thank you for contributing to the vLLM project.
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🚀

[ywang96]

@simon-mo WDYT of this PR? I think it makes sense to me to unify the management of HTTP connections.

[simon-mo]

Code style wise, I would prefer something like get_global_http_client get_global_async_http_client instead of a seemingly constant variable.

But good direction!

[DarkLight1337]

Code style wise, I would prefer something like get_global_http_client get_global_async_http_client instead of a seemingly constant variable.

But good direction!

See if f4cfb65 suits you.

[DarkLight1337]

Any update? @simon-mo

[hmellor]

I'm not 100% sure how, but this PR appears to have broken the dev documentation.

Setup environment:

cd docs
python -m venv venv
. venv/bin/activate
pip install -r requirements-docs.txt

Start HTTP server:

python -m http.server -d build/html/

Checkout commit prior to this PR and build:

git checkout c051bfe4eb77b82eba90504360bbd4e61d9e489a
make clean && make html

Navigate to http://localhost:8001/dev/sampling_params.html and see a populated page.

Checkout merge commit from this PR and build:

git checkout 97234be0ec67f48ed5e65bc0290f329dfb33798e
make clean && make html

Navigate to http://localhost:8001/dev/sampling_params.html and see an empty page.