Required fields that are conditionally shown/hidden shouldn't required data unless shown

@polevaultweb

This is related to WPUserManager/wpum-custom-fields#71
I need to add filter in validate_fields function to allow skip field validation.

Author: reygcalantaol

includes/abstracts/abstract-wpum-form.php

@@ -298,6 +298,10 @@ protected function str_len( $str ) {
 	protected function validate_fields( $values ) {
 		foreach ( $this->fields as $group_key => $group_fields ) {
 			foreach ( $group_fields as $key => $field ) {
+				// Skip validation if field conditional logic not met.
+				if ( apply_filters( 'wpum_form_skip_field_validation', false, $key, $values[ $group_key ], $group_fields ) ) {
+					continue;
+				}
 				if ( $field['required'] && empty( $values[ $group_key ][ $key ] ) ) {
 					return new WP_Error( 'validation-error', sprintf( __( '%s is a required field', 'wp-user-manager' ), $field['label'] ) );
 				}