[TEC-4931] Change client initialization in OrderSync to have the sess…

…ion_id specified in default headers

This is a workaround for Missing Session AuthScema proposed by the flow.io dev - flowcommerce/ruby-sdk#26 (review)

Allows to update flowcommerce gem, not depending on a fork.

app/services/flowcommerce_spree/order_sync.rb

@@ -27,7 +27,10 @@ def initialize(order:)
 
       @experience = order.flow_io_experience_key
       @order = order
-      @client = FlowcommerceSpree.client(session_id: fetch_session_id)
+      @client = FlowcommerceSpree.client(
+        default_headers: { "Authorization": "Session #{fetch_session_id}" },
+        authorization: nil
+      )
     end
 
     # helper method to send complete order from Spree to flow.io