[Frontend] Expose custom args in OpenAI APIs (#16862)

Signed-off-by: Andrew Feldman <afeldman@neuralmagic.com>
Signed-off-by: Andrew Feldman <afeldman@redhat.com>
Co-authored-by: Nick Hill <nhill@redhat.com>

vllm/sampling_params.py

@@ -198,8 +198,8 @@ class SamplingParams(
             processor which only retains scores for the given token ids.
             Defaults to None.
         extra_args: Arbitrary additional args, that can be used by custom
-            sampling implementations. Not used by any in-tree sampling
-            implementations.
+            sampling implementations, plugins, etc. Not used by any in-tree
+            sampling implementations.
     """
 
     n: int = 1