feat: Add responses and safety impl extra_body (#3781)

# What does this PR do?

Have closed the previous PR due to merge conflicts with multiple PRs
Addressed all comments from
https://github.com/llamastack/llama-stack/pull/3768 (sorry for carrying
over to this one)


## Test Plan
Added UTs and integration tests

llama_stack/apis/agents/openai_responses.py

@@ -131,8 +131,20 @@ class OpenAIResponseOutputMessageContentOutputText(BaseModel):
     annotations: list[OpenAIResponseAnnotations] = Field(default_factory=list)
 
 
+@json_schema_type
+class OpenAIResponseContentPartRefusal(BaseModel):
+    """Refusal content within a streamed response part.
+
+    :param type: Content part type identifier, always "refusal"
+    :param refusal: Refusal text supplied by the model
+    """
+
+    type: Literal["refusal"] = "refusal"
+    refusal: str
+
+
 OpenAIResponseOutputMessageContent = Annotated[
-    OpenAIResponseOutputMessageContentOutputText,
+    OpenAIResponseOutputMessageContentOutputText | OpenAIResponseContentPartRefusal,
     Field(discriminator="type"),
 ]
 register_schema(OpenAIResponseOutputMessageContent, name="OpenAIResponseOutputMessageContent")
@@ -878,18 +890,6 @@ class OpenAIResponseContentPartOutputText(BaseModel):
     logprobs: list[dict[str, Any]] | None = None
 
 
-@json_schema_type
-class OpenAIResponseContentPartRefusal(BaseModel):
-    """Refusal content within a streamed response part.
-
-    :param type: Content part type identifier, always "refusal"
-    :param refusal: Refusal text supplied by the model
-    """
-
-    type: Literal["refusal"] = "refusal"
-    refusal: str
-
-
 @json_schema_type
 class OpenAIResponseContentPartReasoningText(BaseModel):
     """Reasoning text emitted as part of a streamed response.