Support for Multiple Custom Plugin Scripts in froala_widget.html.twig

### Description
The README suggests that multiple custom plugin and button scripts can be loaded using the customJS option:

```yaml
# Custom JS file.
# Usage: add custom plugins/buttons...
customJS: "/custom/js/path"
```

However, the `src/Resources/views/Form/froala_widget.html.twig` file currently only accommodates a single string for the froala_customJS variable:
```twig
{% if froala_customJS is defined %}

{% endif %}
```

Additionally, as referenced in [Issue #127](https://github.com/froala/KMSFroalaEditorBundle/issues/127), the correct variable name passed to asset() should be froala_customJS.

### Problem
This implementation does not allow for an array of scripts to be passed and iterated through, which limits flexibility for users who need to load multiple scripts.

### Suggested Solution
Update the Twig template to handle both a single string and an array of scripts for froala_customJS. The logic should maintain backward compatibility, loading a single script if a string is provided or iterating through an array if multiple scripts are specified. Below is the proposed code update:
```twig
{% if froala_customJS is defined %}
{% if froala_customJS is iterable %}
{% for script in froala_customJS %}

{% endfor %}
{% else %}

{% endif %}
{% endif %}
```

### Benefits
- Supports both single string and array formats for froala_customJS.
- Maintains backward compatibility with existing implementations.
- Provides greater flexibility for users to load multiple custom plugins or buttons.