DashGPT: Use single prompt to generate title and descriptions

[ivanortegaalba]

Not all DashGPT features work nicely with non-OpenAI models (in particular Dashboard title generation just returns the system prompt when used with Llama3)
The reason for that is that llama3 in particular (and maybe other LLMs) expect at most a single system prompt. In DashGPT we seem to be using a combination of
multiple system prompts + user prompts
multiple system prompts and no user prompt at all
Was wondering if we can update the structure prompts to have
1 single system prompt
1 single user prompt
As part of the blog post for ☝️, was planning to do some benchmarking so we could use that to check the impact on outputs, but changing just the structure and not the prompts itself should have minimal impact