Remove order promotions promotion code value from search key

Removing "_or_order_promotions_promotion_code_value" from the `order_search_key`
preference.
This part of the search key was causing exceptions during pagination due
to missing columns in the SQLite database.
Specifically, the exception was :
"ActiveRecord::StatementInvalid (SQLite3::SQLException: no such column: order_promotions_spree_orders.promotion_code_id)".

Note: This bug fix will be evaluated in a separate PR.

admin/lib/solidus_admin/configuration.rb

@@ -75,10 +75,10 @@ class Configuration < Spree::Preferences::Configuration
  # The key that specifies the attributes for searching orders within the admin interface.
  # This preference controls which attributes of an order are used in search queries.
  # By default, it is set to
- # 'number_shipments_number_or_bill_address_name_or_email_order_promotions_promotion_code_value_cont',
- # enabling a search across order number, shipment number, billing address name, email, and promotion code value.
+ # 'number_or_shipments_number_or_bill_address_name_or_email_cont',
+ # enabling a search across order number, shipment number, billing address name, email.
  # @return [String] The search key used to determine order attributes for search.
- preference :order_search_key, :string, default: :number_or_shipments_number_or_bill_address_name_or_email_or_order_promotions_promotion_code_value_cont
+ preference :order_search_key, :string, default: :number_or_shipments_number_or_bill_address_name_or_email_cont
 
  # @!attribute [rw] products_per_page
  # @return [Integer] The number of products to display per page in the admin interface.