Remove the usage of eCPC bidding because of its deprecation (#465)

examples/shopping_ads/add_shopping_product_ad.rb

@@ -96,8 +96,13 @@ def add_standard_shopping_campaign(
 
     campaign.status = :PAUSED
 
+    # Sets the bidding strategy to Manual CPC (with eCPC disabled). eCPC for standard
+    # Shopping campaigns is deprecated. If eCPC is set to true, Google Ads ignores the
+    # setting and behaves as if the setting was false. See this blog post for more
+    # information:
+    # https://ads-developers.googleblog.com/2023/09/google-ads-shopping-campaign-enhanced.html
     campaign.manual_cpc = client.resource.manual_cpc do |manual_cpc|
-      manual_cpc.enhanced_cpc_enabled = true
+      manual_cpc.enhanced_cpc_enabled = false
     end
 
     campaign.campaign_budget = budget_name