Fix: generate endpoint form model

According to the [Ollama documentation] the parameter `context` should be an array of int, if specified.

backend/open_webui/apps/ollama/main.py

@@ -692,7 +692,7 @@ class GenerateCompletionForm(BaseModel):
     options: Optional[dict] = None
     system: Optional[str] = None
     template: Optional[str] = None
-    context: Optional[str] = None
+    context: Optional[list[int]] = None
     stream: Optional[bool] = True
     raw: Optional[bool] = None
     keep_alive: Optional[Union[int, str]] = None