Improve prompting for diffusers default snippets

[apolinario]

Addressing comments left on #907, specially for LoRAs

[mishig25]

looking great!

regarding this line:

prompt = "${get_prompt_from_diffusers_model(model) ?? diffusersDefaultPrompt}"

I think there can be edge case where user supplied prompt has quote like ", which means we need to escape ".
Otherwise, there is a danger of producing broken python code like:

prompt = "Astronaut holding sign that says "Hello"" # which is that it is now

prompt = "Astronaut holding sign that says \"Hello\"" # which is what it should be

[Vaibhavs10]

Conceptually looks great to me! Thanks for taking this to the finish line! 🐐