Hide optional configuration fields

https://redmine.teklia.com/issues/7498

Worker versions often have incomprehensible user configurations with five trillion parameters, because Machine Learning™. Most of those parameters have default values, and users who only intend to run some simple ML task do not need to care about them. We can make running training or inference processes simpler by hiding everything that most people won't need.

Please split the WorkerConfiguration form into two <DropdownContent>:

• Required configuration, opened by default, which contains the required fields that do not have a default value;
• Optional configuration, closed by default, which contains every other field.

Fields are currently sorted alphabetically by title, and they still should be, just within each of the sections.

When there are no fields in one of the two sections, a Bulma notification should be displayed to explain that there's nothing to see here.