[Do Not Merge] Change default of external event publishing

[rbev]

Important

Targeted for 7.0, should not be merged to master until it is time to mark that branch for the major update

This pull request updates the configuration for external integrations publishing to use a new positive EnableExternalIntegrationsPublishing setting instead of the previous negative DisableExternalIntegrationsPublishing flag. It also ensures backward compatibility with the legacy setting, adds comprehensive unit tests for the new logic, and updates documentation and acceptance tests accordingly.

Configuration and Feature Flag Changes:

• Replaces the DisableExternalIntegrationsPublishing flag with EnableExternalIntegrationsPublishing throughout the codebase, updating all conditionals and configuration checks to use the new positive flag. [1] [2] [3] [4]
• Updates documentation to reflect the new ServiceControl/EnableExternalIntegrationsPublishing setting, while still supporting the legacy ServiceControl/DisableExternalIntegrationsPublishing as an inverted alternative.

Testing and Backward Compatibility:

• Adds a new unit test class ExternalIntegrationsPublishingSettingsTests to verify the correct behavior of the new and legacy settings, including error handling when both are set.
• Updates all relevant acceptance tests to explicitly enable external integrations publishing using the new setting for consistent test behavior.