Implement LLM Chat API with tool calling support (#21731)

* Implement initial tools definiton APIs

* Add initial chat completion API with tool support

* Implement other providers

* Cleanup

frigate/api/defs/request/chat_body.py

@@ -0,0 +1,34 @@
+"""Chat API request models."""
+
+from typing import Optional
+
+from pydantic import BaseModel, Field
+
+
+class ChatMessage(BaseModel):
+    """A single message in a chat conversation."""
+
+    role: str = Field(
+        description="Message role: 'user', 'assistant', 'system', or 'tool'"
+    )
+    content: str = Field(description="Message content")
+    tool_call_id: Optional[str] = Field(
+        default=None, description="For tool messages, the ID of the tool call"
+    )
+    name: Optional[str] = Field(
+        default=None, description="For tool messages, the tool name"
+    )
+
+
+class ChatCompletionRequest(BaseModel):
+    """Request for chat completion with tool calling."""
+
+    messages: list[ChatMessage] = Field(
+        description="List of messages in the conversation"
+    )
+    max_tool_iterations: int = Field(
+        default=5,
+        ge=1,
+        le=10,
+        description="Maximum number of tool call iterations (default: 5)",
+    )