featu: support passing "extra body" throught to providers

# What does this PR do?
Allows passing through extra_body parameters to inference providers.


closes #2720

## Test Plan
CI and added new test

docs/static/stainless-llama-stack-spec.yaml

@@ -5667,18 +5667,6 @@ components:
         user:
           type: string
           description: (Optional) The user to use.
-        guided_choice:
-          type: array
-          items:
-            type: string
-          description: >-
-            (Optional) vLLM-specific parameter for guided generation with a list of
-            choices.
-        prompt_logprobs:
-          type: integer
-          description: >-
-            (Optional) vLLM-specific parameter for number of log probabilities to
-            return for prompt tokens.
         suffix:
           type: string
           description: >-