Add fields filter for Elementor checkout widget

Please add a filter for widget custom fields, like for custom messages.

In sellkit/includes/elementor/modules/checkout/fields/base.php:66 add,

// Filter label to adjust custom text.

//$label = $args['label'];

$label = eschtml( applyfilters( 'sellkit_core/widgets/checkout/field/label', $args['label'], $args ) );

And on line 196,

// Filter label to adjust custom text.

//$placeholder = ( arraykeyexists( 'label', $args ) )

// ? $args['label']

// : '';

$placeholder = ( arraykeyexists( 'label', $args ) )

? esc_html( apply_filters( 'sellkit_core/widgets/checkout/field/label', $args['label'], $args ) ): '';