[Datasets] Add pyiceberg docs

[lhoestq]

New:

• PyIceberg docs (preview: https://moon-ci-docs.huggingface.co/docs/hub/pr_2212/en/datasets-pyiceberg)

Updated:

• DuckDB docs (preview: https://moon-ci-docs.huggingface.co/docs/hub/pr_2212/en/datasets-duckdb)

cc @kszucs

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Note

Low Risk
Low risk: documentation-only changes, but adds new guidance and examples that could confuse users if commands/URIs are inaccurate.

Overview
Adds new PyIceberg documentation describing how to use faceberg to deploy an Iceberg datasets catalog on Spaces, authenticate, add Hub datasets, and query them via faceberg or native pyiceberg REST catalog clients.

Updates DuckDB docs to include a dedicated authentication section, refreshed hf:// querying examples/output, and a new section showing how to query datasets through an Iceberg catalog (faceberg.namespace.dataset) including split-based filtering and catalog deployment steps.

Navigation/index updates: adds PyIceberg (and PyArrow) entries to the datasets libraries toctree and lists PyIceberg in the libraries table.

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[HuggingFaceDocBuilderDev]

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[davanstrien]

@lhoestq want a review on this? I think there are some outstanding TODOs in the PR still?

[lhoestq]

I removed the todo which was not necessary :p

Anyways while this is useful for datasets already, I think content on iceberg will be mostly relevant for buckets in the future

lmk what you think !