feat(prompts): Load prompt into playground via url (#5893)

* feat(prompts): Load prompt into playground via url

* Parse prompt version data into playground instance format

* Move prompt to instance conversion deeper into component tree

This allows us to pre-fill the default instance with a prompt from the URL,
while also allowing for the loaded prompt to be dynamically switched (fetched) per-instance

* Perform prompt fetch imperatively instead of declaratively

* Simplify prompt change callback

* Rename loader