Responses API: Delete a response API endpoint

[bbrowning]

🚀 Describe the new functionality needed

We're missing the API endpoint to delete Responses from the conversation state - see https://platform.openai.com/docs/api-reference/responses/delete .

💡 Why is this needed? What if we don't build it?

It's part of the Responses API, so would be needed for 100% coverage. I don't know how often it would be used with Llama Stack, but for completeness sake and because it shouldn't be a large lift, we should probably implement it.

Other thoughts

No response