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* [doc] performance/scalability revamp

* link the new docs

* no :

* mixed precision

* work on the first doc

* expand the main doc

* Trigger CI

* style

* revamp single GPU training section

* work on training performance

* remove files not used anymore or will be added later

* final touches

* fix rebase

* Add hardware section to toctree

* fix toctree again

* Apply suggestions from code review
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* remove `fast_tokenizers` entry that was copied in rebase

* add warning about DP vs DDP

* remove todo

* Apply suggestions from code review
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* fix missing closure of codeblock

* Update docs/source/en/perf_train_gpu_many.mdx
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* sync with #16860

* update toc
Co-authored-by: leandro <leandro.vonwerra@spoud.io>
Co-authored-by: Leandro von Werra <lvwerra@users.noreply.github.com>
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>