Load PEFT weights from local directory (#1260)

# What does this PR do?

Enables PEFT weights to be loaded from a local directory, as opposed to
a hf hub repository. It is a continuation of the work in PR
https://github.com/huggingface/text-generation-inference/pull/762

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Fixes #1259 


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the
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@Narsil 

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---------

Co-authored-by: Nicolas Patry <patry.nicolas@protonmail.com>

server/text_generation_server/cli.py

@@ -150,6 +150,17 @@ def download_weights(
             if not extension == ".safetensors" or not auto_convert:
                 raise e
 
+    else:
+        # Try to load as a local PEFT model
+        try:
+            utils.download_and_unload_peft(
+                model_id, revision, trust_remote_code=trust_remote_code
+            )
+            utils.weight_files(model_id, revision, extension)
+            return
+        except (utils.LocalEntryNotFoundError, utils.EntryNotFoundError):
+            pass
+
     # Try to see if there are local pytorch weights
     try:
         # Get weights for a local model, a hub cached model and inside the WEIGHTS_CACHE_OVERRIDE