feat(api)!: BREAKING CHANGE: support passing extra_body through to providers (#3777)

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

With this, we removed the 2 vllm-specific parameters from completions
API into `extra_body`.
Before/After
<img width="1883" height="324" alt="image"
src="https://github.com/user-attachments/assets/acb27c08-c748-46c9-b1da-0de64e9908a1"
/>



closes #2720

## Test Plan
CI and added new test
```
❯ uv run pytest -s -v tests/integration/ --stack-config=server:starter --inference-mode=record -k 'not( builtin_tool or safety_with_image or code_interpreter or test_rag ) and test_openai_completion_guided_choice' --setup=vllm --suite=base --color=yes
Uninstalled 3 packages in 125ms
Installed 3 packages in 19ms
INFO     2025-10-10 14:29:54,317 tests.integration.conftest:118 tests: Applying setup 'vllm' for suite base
INFO     2025-10-10 14:29:54,331 tests.integration.conftest:47 tests: Test stack config type: server
         (stack_config=server:starter)
============================================================================================================== test session starts ==============================================================================================================
platform darwin -- Python 3.12.11, pytest-8.4.2, pluggy-1.6.0 -- /Users/erichuang/projects/llama-stack-1/.venv/bin/python
cachedir: .pytest_cache
metadata: {'Python': '3.12.11', 'Platform': 'macOS-15.6.1-arm64-arm-64bit', 'Packages': {'pytest': '8.4.2', 'pluggy': '1.6.0'}, 'Plugins': {'anyio': '4.9.0', 'html': '4.1.1', 'socket': '0.7.0', 'asyncio': '1.1.0', 'json-report': '1.5.0', 'timeout': '2.4.0', 'metadata': '3.1.1', 'cov': '6.2.1', 'nbval': '0.11.0'}}
rootdir: /Users/erichuang/projects/llama-stack-1
configfile: pyproject.toml
plugins: anyio-4.9.0, html-4.1.1, socket-0.7.0, asyncio-1.1.0, json-report-1.5.0, timeout-2.4.0, metadata-3.1.1, cov-6.2.1, nbval-0.11.0
asyncio: mode=Mode.AUTO, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function
collected 285 items / 284 deselected / 1 selected

tests/integration/inference/test_openai_completion.py::test_openai_completion_guided_choice[txt=vllm/Qwen/Qwen3-0.6B]
instantiating llama_stack_client
Starting llama stack server with config 'starter' on port 8321...
Waiting for server at http://localhost:8321... (0.0s elapsed)
Waiting for server at http://localhost:8321... (0.5s elapsed)
Waiting for server at http://localhost:8321... (5.1s elapsed)
Waiting for server at http://localhost:8321... (5.6s elapsed)
Waiting for server at http://localhost:8321... (10.1s elapsed)
Waiting for server at http://localhost:8321... (10.6s elapsed)
Server is ready at http://localhost:8321
llama_stack_client instantiated in 11.773s
PASSEDTerminating llama stack server process...
Terminating process 98444 and its group...
Server process and children terminated gracefully


============================================================================================================= slowest 10 durations ==============================================================================================================
11.88s setup    tests/integration/inference/test_openai_completion.py::test_openai_completion_guided_choice[txt=vllm/Qwen/Qwen3-0.6B]
3.02s call     tests/integration/inference/test_openai_completion.py::test_openai_completion_guided_choice[txt=vllm/Qwen/Qwen3-0.6B]
0.01s teardown tests/integration/inference/test_openai_completion.py::test_openai_completion_guided_choice[txt=vllm/Qwen/Qwen3-0.6B]
================================================================================================ 1 passed, 284 deselected, 3 warnings in 16.21s =================================================================================================
```

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

@@ -1098,7 +1098,7 @@ paths:
         content:
           application/json:
             schema:
-              $ref: '#/components/schemas/OpenAIChatCompletionRequest'
+              $ref: '#/components/schemas/OpenAIChatCompletionRequestWithExtraBody'
         required: true
       deprecated: true
   /v1/openai/v1/chat/completions/{completion_id}:
@@ -1167,7 +1167,7 @@ paths:
         content:
           application/json:
             schema:
-              $ref: '#/components/schemas/OpenAICompletionRequest'
+              $ref: '#/components/schemas/OpenAICompletionRequestWithExtraBody'
         required: true
       deprecated: true
   /v1/openai/v1/embeddings:
@@ -5575,7 +5575,7 @@ components:
       title: OpenAIResponseFormatText
       description: >-
         Text response format for OpenAI-compatible chat completion requests.
-    OpenAIChatCompletionRequest:
+    OpenAIChatCompletionRequestWithExtraBody:
       type: object
       properties:
         model:
@@ -5717,7 +5717,7 @@ components:
       required:
         - model
         - messages
-      title: OpenAIChatCompletionRequest
+      title: OpenAIChatCompletionRequestWithExtraBody
       description: >-
         Request parameters for OpenAI-compatible chat completion endpoint.
     OpenAIChatCompletion:
@@ -5885,7 +5885,7 @@ components:
         - model
         - input_messages
       title: OpenAICompletionWithInputMessages
-    OpenAICompletionRequest:
+    OpenAICompletionRequestWithExtraBody:
       type: object
       properties:
         model:
@@ -5973,18 +5973,6 @@ 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: >-
@@ -5993,7 +5981,7 @@ components:
       required:
         - model
         - prompt
-      title: OpenAICompletionRequest
+      title: OpenAICompletionRequestWithExtraBody
       description: >-
         Request parameters for OpenAI-compatible completion endpoint.
     OpenAICompletion: