Promotions: Set line_item_option_value product-picker multiple false

This updates the product picker for the line_item_option_value form
to not allow selecting multiple products per entry.

Author: manleyac

promotions/app/javascript/backend/solidus_promotions/web_components/product_picker.js

@@ -1,6 +1,7 @@
 class ProductPicker extends HTMLInputElement {
   connectedCallback() {
-    $(this).productAutocomplete();
+    const multiple = this.dataset.multiple !== "false";
+    $(this).productAutocomplete({ multiple });
   }
 }
 

promotions/lib/views/backend/solidus_promotions/admin/condition_fields/line_item_option_value/_option_value_fields.html.erb

@@ -4,6 +4,7 @@
       is="product-picker"
       class="w-100"
       data-action="select2Change->product-option-values#propagate_product_id_to_value_input"
+      data-multiple="false"
       type="hidden"
       value="<%= product_option_values[0] %>"
     >