Add wrapper class option to grid style.

Closes #3195981

src/Plugin/views/style/ViewsBootstrapGrid.php

@@ -41,6 +41,7 @@ class ViewsBootstrapGrid extends StylePluginBase {
   protected function defineOptions() {
     $options = parent::defineOptions();
 
+    $options['wrapper_class'] = ['default' => ''];
     foreach (ViewsBootstrap::getBreakpoints() as $breakpoint) {
       $breakpoint_option = "col_$breakpoint";
       $options[$breakpoint_option] = ['default' => 'none'];
@@ -66,6 +67,13 @@ class ViewsBootstrapGrid extends StylePluginBase {
   public function buildOptionsForm(&$form, FormStateInterface $form_state) {
     parent::buildOptionsForm($form, $form_state);
 
+    $form['wrapper_class'] = [
+      '#type' => 'textfield',
+      '#title' => $this->t('Wrapper class'),
+      '#default_value' => $this->options['wrapper_class'],
+      '#description' => $this->t('Add a class to the .row element surrounding the results. <a href="https://getbootstrap.com/docs/4.5/utilities/flex/" target="_blank">Bootstrap\'s flex utilities</a>, for example.'),
+    ];
+
     foreach (ViewsBootstrap::getBreakpoints() as $breakpoint) {
       $breakpoint_option = "col_$breakpoint";
       $prefix = 'col' . ($breakpoint != 'xs' ? '-' . $breakpoint : '');