Add missing 'include' for major upgrade guide general advice

Include missing major upgrade general advice for 7 to 8 and 8 to 9 major upgrades.

Author: warwickschroeder

nservicebus/upgrades/7to8/index.md

@@ -9,6 +9,8 @@ upgradeGuideCoreVersions:
  - 8
 ---
 
+include: upgrade-major
+
 This document focuses on changes that are affecting general endpoint configuration and message handlers. For more upgrade guides, see the following additional guides:
 
 * [Changes for downstream implementations like custom/community transports, persistence, message serializers](implementations.md)

nservicebus/upgrades/8to9/index.md

@@ -9,6 +9,8 @@ upgradeGuideCoreVersions:
  - 9
 ---
 
+include: upgrade-major
+
 ## Removed support for .NET Framework
 
 NServiceBus 9 no longer supports any version of the .NET Framework. Instead, it targets .NET 8 only (read more about the [supported frameworks and platforms](/nservicebus/upgrades/supported-platforms.md)). Any component in NServiceBus 8 that is .NET Framework only (for example, the MSMQ transport) will not have a version that is compatible with NServiceBus 9. NServiceBus 8 will continue to be supported for use on the .NET Framework.