AWS Elastic CI Stack v5.19.0 release

The v5.19.0 version of the Elastic CI Stack is now avaliable. This includes a fix for an error encountered when creating a new stack from its cloudformation template due to an attempt to create an ACL for object ownership when they are now disabled by default.

For further details of the fix and what else is included in the release, see the Elastic CI Stack's release notes.