Automatic form generation for Config Entities with customizing design by the configuration

Problem/Motivation

When we create a custom config entity, we should define the schema for the data, so basically describe each field - data type, label, description.

But to create the add/edit form, we have to create a form, where should describe the entity's fields again!

Sounds not good, right? Let's simplify this!

Proposed resolution

The idea is to get the config entity schema and automatically generate the add/edit form for the custom entity. With this, all that you have to do is just configure the form handles in your custom configuration form like this:

#[ConfigEntityType(
  id: 'schema_form_design',
  ...
  handlers: [
    'form' => [
      'add' => SchemaFormEntityForm::class,
      'edit' => SchemaFormEntityForm::class,
      'delete' => EntityDeleteForm::class,
    ],
  ],

and that's it!

Also, introduce a configuration entity "Schema Form Design" that will contain the additional information related to the form building process, which will be applied to the form. This approach should allow the customization of the schema forms by extending and overriding the automatically generated form elements, without using custom code.