Enhancements and bug fixes

The following changes are included in this release.

Allowed domains for notifications. Users are now able to add/remove domains that are allowed to receive email notifications.

Configurable default access agreement message. Users can now configure a default top level access agreement message using the xpack.security.accessAgreement.message setting. This access agreement message will display for any providers that do not specify a local access agreement message.

Correctly remove incompatible extensions on upgrade. Upgrades for deployments that use custom extensions should no longer fail if an extension is incompatible with the target version.

Always remove the topology element plugin and bundle properties, regardless of whether anything had to be migrated. Fixed an issue where customers could not enable plugins on existing deployments.

Improved instance health checker. Fixed a bug where the deployment health indicator would incorrectly show instances as unhealthy when deployments were terminated or deleted.