Allow LoRA adapter revision in server launcher

[teamclouday]

What does this PR do?

I was trying to load an adapter from hub with specific revision. The document about revision is missing but by checking the code there's support in the format of adapter_id=path@revision. Details can be found in parse_lora_adapters method and test code.

However, setting the revision doesn't work because the launcher will try to download the model first, and it's ignoring revision. Therefore I'm making this PR hoping to enable adapter revision. Also added documentation of the adapter revision format.

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[teamclouday]

Also wonder if there exists implementation to dynamically download the lora adapter when being requested from API

[HuggingFaceDocBuilderDev]

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[drbh]

Hi @teamclouday thank you for this contribution and fix! I've just merged the changes after rerunning CI in this PR #2602. Thank you!

Regarding downloading the adapter at request time - this is currently out of scope for TGI because we aim to statically allocate memory at startup. Currently we avoid any dynamic allocations at runtime. Downloading an adapter and loading after startup would violate this constraint and will likely not be supported.

[teamclouday]

Thank you! That makes sense!