Default to Qwen3 in README.md and docs/ examples

[alvarobartt]

What does this PR do?

This PR updates the default --model-id value showed within the example in the README.md and the docs/ so as to point to the recently released and integrated Qwen/Qwen3-Embedding-0.6B (from the Qwen3-Embedding collection), due to its small size compared to other more performant alternatives, making it available on CPU, MPS and GPUs seamlessly, and with an MTEB mean score of 64.33 way above other alternatives with bigger or the same size.

Additionally, this PR also aligns the "Supported models" tables in the README.md and in docs/source/en/supported_models.md to show the same content.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline, Pull Request section?
• Was this discussed/approved via a GitHub issue or the forum? Please add a link to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the documentation guidelines, and here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

@Narsil

[Narsil]

LGTM

[HuggingFaceDocBuilderDev]

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