docs: fetch external sources

[Borda]

What does this PR do?

making docs as standalone resources without needing to pull S3 assets
pending on Lightning-AI/utilities#142

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• Did you make sure to update the documentation with your changes? (if necessary)
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• Did you verify new and existing tests pass locally with your changes?
• Did you list all the breaking changes introduced by this pull request?
• Did you update the CHANGELOG? (not for typos, docs, test updates, or minor internal changes/refactors)

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cc @Borda @tchaton @carmocca @justusschock @awaelchli

[github-actions]

⚡ Required checks status: All passing 🟢

Groups summary

🟢 fabric: Docs

Check ID	Status
make-doctest (fabric)	success	✅
make-html (fabric)	success	✅

These checks are required after the changes to docs/source-fabric/conf.py, docs/source-fabric/fundamentals/accelerators.rst, docs/source-fabric/fundamentals/launch.rst, docs/source-fabric/fundamentals/precision.rst, requirements/docs.txt.

🟢 pytorch_lightning: Docs

Check ID	Status
make-doctest (pytorch)	success	✅
make-html (pytorch)	success	✅

These checks are required after the changes to docs/source-pytorch/accelerators/gpu_intermediate.rst, docs/source-pytorch/accelerators/tpu_basic.rst, docs/source-pytorch/advanced/speed.rst, docs/source-pytorch/common/early_stopping.rst, docs/source-pytorch/common/trainer.rst, docs/source-pytorch/conf.py, docs/source-pytorch/data/datamodule.rst, docs/source-pytorch/debug/debugging_basic.rst, docs/source-pytorch/model/build_model_intermediate.rst, docs/source-pytorch/starter/introduction.rst, requirements/docs.txt.

🟢 lightning_app: Docs

Check ID	Status
make-doctest (app)	success	✅
make-html (app)	success	✅

These checks are required after the changes to docs/source-app/conf.py, docs/source-app/examples/file_server/file_server_content.rst, docs/source-app/examples/github_repo_runner/github_repo_runner_content.rst, docs/source-app/get_started/go_beyond_training_content.rst, docs/source-app/get_started/jumpstart_from_app_gallery.rst, docs/source-app/get_started/what_app_can_do.rst, docs/source-app/glossary/secrets.rst, docs/source-app/glossary/storage/path.rst, docs/source-app/levels/intermediate/level_9.rst, docs/source-app/workflows/build_command_line_interface/cli_client.rst, docs/source-app/workflows/build_rest_api/add_api.rst, docs/source-app/workflows/byoc/aws_console.rst, requirements/docs.txt.

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Thank you for your contribution! 💜

Note
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[Borda]

okk, it seems that Sphinx does not include resources linked only in HTML section

.. raw:: html

    <video width="50%" max-width="400px" controls
    poster="https://pl-bolts-doc-images.s3.us-east-2.amazonaws.com/pl_docs/trainer_flags/thumb/check_val_every_n_epoch.jpg"
    src="https://pl-bolts-doc-images.s3.us-east-2.amazonaws.com/pl_docs/trainer_flags/check_val_every_n_epoch.mp4"></video>

Consider replacement with https://github.com/sphinx-contrib/video
checking sphinx-contrib/video#26

[carmocca]

There's no docs preview so I don't really know what I'm approving 🤞

[Borda]

There's no docs preview so I don't really know what I'm approving crossed_fingers

there is, see the checks: https://pytorch-lightning--17941.org.readthedocs.build/en/17941/