[Misc] Improve model redirect to accept json dictionary

[Isotr0py]

• Following PR for [Misc] Use model_redirect to redirect the model name to a local folder. #14116.
• It's not very useful if the model redirection only accepts tab-separated values, because some IDEs like vscode will replace tab with four spaces for indent.
• This PR allows using json file and space-separated table for model redirection.

Examples:

$ VLLM_MODEL_REDIRECT_PATH=./model_redirect.json pytest -s -v tests/models/test_initialization.py -k Florence2ForConditionalGeneration
INFO 04-06 14:05:32 [__init__.py:239] Automatically detected platform cpu.
=================================================================================== test session starts ===================================================================================
platform linux -- Python 3.12.8, pytest-8.3.4, pluggy-1.5.0 -- /data/develop-projects/github-repos/vllm-cpu/.venv/bin/python
cachedir: .pytest_cache
rootdir: /data/develop-projects/github-repos/vllm-cpu
configfile: pyproject.toml
plugins: anyio-4.8.0, typeguard-4.3.0
collected 131 items / 130 deselected / 1 selected                                                                                                                                         

tests/models/test_initialization.py::test_can_initialize[Florence2ForConditionalGeneration]
INFO 04-06 14:05:34 [utils.py:95] model redirect: [ microsoft/Florence-2-base ] -> [ /data/LLM-model/Florence-2-base ]
INFO 04-06 14:05:34 [utils.py:95] model redirect: [ facebook/bart-base ] -> [ /data/LLM-model/bart-base ]

[github-actions]

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

💬 Join our developer Slack at https://slack.vllm.ai to discuss your PR in #pr-reviews, coordinate on features in #feat- channels, or join special interest groups in #sig- channels.

Just a reminder: PRs would not trigger full CI run by default. Instead, it would only run fastcheck CI which starts running only a small and essential subset of CI tests to quickly catch errors. You can run other CI tests on top of those by going to your fastcheck build on Buildkite UI (linked in the PR checks section) and unblock them. If you do not have permission to unblock, ping simon-mo or khluu to add you in our Buildkite org.

Once the PR is approved and ready to go, your PR reviewer(s) can run CI to test the changes comprehensively before merging.

To run CI, PR reviewers can either: Add ready label to the PR or enable auto-merge.

🚀

[DarkLight1337]

Can you fix the pre-commit errors? Otherwise LGTM