Add is_required column to pp_shop_products_custom_fields table

This commit introduces a new column `is_required` to the `pp_shop_products_custom_fields` table. The column is of type TINYINT, cannot be null, and has a default value of 1. This change is intended to enhance the product custom fields by allowing the specification of whether a field is mandatory.

admin/layout/style-scss/style.scss

@@ -2228,4 +2228,20 @@ textarea.form-control {
     width: 50px;
     text-align: center;
   }
+}
+
+.input-group-addon {
+  width: auto;
+
+  label {
+    display: flex;
+    align-items: center;
+    gap: 5px;
+  }
+}
+
+.additional_fields {
+  input[type="text"] {
+    height: 40px;
+  }
 }