Remove the usage of eCPC bidding because of its deprecation

To align with the [code example change](googleads/google-ads-java#742) requested for the Java client library.

As seen in this [blog announcement](https://ads-developers.googleblog.com/2023/09/google-ads-shopping-campaign-enhanced.html), any Shopping campaigns using Enhanced cost-per-click (eCPC) will behave as if they are using Manual cost-per-click (CPC) bidding.

Because of the change, I'm updating the examples related to the announcement to reflect the new recommended practice.

examples/shopping_ads/add_shopping_product_ad.py

@@ -187,11 +187,15 @@ def add_standard_shopping_campaign(
     # and the ads are ready to serve.
     campaign.status = client.enums.CampaignStatusEnum.PAUSED
 
-    # Sets the bidding strategy to Manual CPC (with eCPC enabled)
+    # 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
     # Recommendation: Use one of the automated bidding strategies for Shopping
     # campaigns to help you optimize your advertising spend. More information
     # can be found here: https://support.google.com/google-ads/answer/6309029
-    campaign.manual_cpc.enhanced_cpc_enabled = True
+    campaign.manual_cpc.enhanced_cpc_enabled = False
 
     # Sets the budget.
     campaign.campaign_budget = budget_resource_name