Fix GradioUI system prompt

On the GradioUI the system prompt displayed is *always* using the
default system prompt, which is problematic when running the service
with a custom system prompt (`system_prompt_path`) and allowing
overriding it (`enable_system_prompt_override: true`).

With this simple patch we default to the configured system prompt on the
GradioUI and only use the default system prompt if we don't have it
configured.

Author: Akrog

ols/src/ui/gradio_ui.py

@@ -34,7 +34,9 @@ def __init__(
         additional_inputs = [use_history, provider, model]
         if config.dev_config.enable_system_prompt_override:
             system_prompt = gr.TextArea(
-                value=prompts.QUERY_SYSTEM_INSTRUCTION, label="System prompt"
+                value=config.ols_config.system_prompt
+                or prompts.QUERY_SYSTEM_INSTRUCTION,
+                label="System prompt",
             )
             additional_inputs.append(system_prompt)
         self.ui = gr.ChatInterface(self.chat_ui, additional_inputs=additional_inputs)