Fix "Trigger again with this config" ignoring param changes made in the UI

[shashbha14]

Closes #67243

When using "Trigger again with this config", any changes made to params in the trigger form were ignored and the original conf from the previous run was submitted instead.

The useEffect that syncs the param store's conf back into the form field had a !prefillConfig guard, which blocked it from running when "Trigger again" was used. So editing a param via the UI updated the store but the form field stayed on the original value.
Removed the guard so the form always stays in sync with the store, and removed prefillConfig from the dependency array since it is no longer used inside that effect.

I used Claude (claude.ai) as an AI assistant for parts of this implementation..

[bbovenzi]

  const { control, handleSubmit, watch } = useForm<DagRunTriggerParams>({
    defaultValues,
    values: { ...defaultValues, conf },
    resetOptions: { keepDirtyValues: true },
  });

Needing two useEffects shows us that there is a problem at the core of how we're handling this. Let's update our use of react-hook-form and then use just one useEffect to handle trigger again.