Add schema definitions for third party for Field Widget Actions

Closes #3538502

• The field_widget_actions module stores its configuration as third-party settings on individual field widgets;
• The configuration has dynamic keys (UUIDs) that can't be predefined in a schema;
• Using type: ignore allows Drupal to accept any structure, which is appropriate for dynamic plugin configurations;
• This follows the same pattern used by ai_automators for its plugin_config;