Copy prompt parameters from custom workflows

[ronan36880]

This change makes it possible to also copy the parameters used in custom workflows. It works by going through all the metadata in the job and sets the matching widget's value.

This makes it so "Copy prompt" will now also work on custom workflows and automatically sets the values on the UI.

I had to implement a signal, but I'm unsure if it's the best approach to doing it, would love some feedback on this if possible.

[Acly]

It might be simpler, can you try:

# custom_workflow.py
class CustomWorkspace:
    def try_set_params(params: dict):
        self.params = _coerce(params, self.metadata)

# ui/generation.py in _copy_prompt
self._model.custom.try_set_params(job.params.metadata)

Should not require the signal, or any changes in the custom param UI part. And it will also take care of cases like having a different workflow which uses a param with the same name, but it has a different type (eg. string instead of number).

Edit: you might want a slightly different version of _coerce which uses the previous value if the job params don't have a match, rather than the default.