fix: OpenAI spec cleanup for assistant requests

Some of our multi-turn verification tests were failing because I had
accidentally marked content as a required field in the OpenAI chat
completion request assistant messages, but it's actually optional. It
is required for messages from other roles, but assistant is explicitly
allowed to be optional.

Similarly, the assistant message tool_calls field should default to None
instead of an empty list.

These two changes get the openai-llama-stack verification test back to
100% passing, just like it passes 100% when not behind Llama Stack.

Signed-off-by: Ben Browning <bbrownin@redhat.com>

docs/_static/llama-stack-spec.html

@@ -8891,8 +8891,7 @@
                 },
                 "additionalProperties": false,
                 "required": [
-                    "role",
+                    "role"
-                    "content"
                 ],
                 "title": "OpenAIAssistantMessageParam",
                 "description": "A message containing the model's (assistant) response in an OpenAI-compatible chat completion request."

docs/_static/llama-stack-spec.yaml

@@ -6097,7 +6097,6 @@ components:
       additionalProperties: false
       required:
         - role
-        - content
       title: OpenAIAssistantMessageParam
       description: >-
         A message containing the model's (assistant) response in an OpenAI-compatible

llama_stack/apis/inference/inference.py

@@ -526,9 +526,9 @@ class OpenAIAssistantMessageParam(BaseModel):
     """
 
     role: Literal["assistant"] = "assistant"
-    content: OpenAIChatCompletionMessageContent
+    content: Optional[OpenAIChatCompletionMessageContent] = None
     name: Optional[str] = None
-    tool_calls: Optional[List[OpenAIChatCompletionToolCall]] = Field(default_factory=list)
+    tool_calls: Optional[List[OpenAIChatCompletionToolCall]] = None
 
 
 @json_schema_type