[Inference Providers] Add DeepInfra inference provider documentation

[hanouticelina]

⚠️ Do not merge until the DeepInfra integration is live

Part of the DeepInfra provider integration (huggingface/huggingface.js#1804).

Logos uploaded to huggingface/documentation-images: deepinfra-light.png, deepinfra-dark.png

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Note

Low Risk
Documentation and static-site generation updates only; no runtime product logic or security-sensitive code paths are changed.

Overview
Adds DeepInfra as a listed Inference Provider by updating the docs navigation (_toctree.yml) and partners table (index.md).

Introduces a generated provider page providers/deepinfra.md and its source template deepinfra.handlebars, and updates the docs generation script (generate.ts) to include DeepInfra in PROVIDERS_URLS so it is rendered alongside other providers.

^{Reviewed by Cursor Bugbot for commit 8f28dd5. Configure here.}

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[Wauplin]

🙌