Add domain-events package to SDK dependencies (#3)

Include complex-heart/domain-events ^1.0.0 in the meta-package.

Feature/Updated SDK dependencies and improved README documentation (#2)

* Contracts upgraded to v3.0.0
* Domain Model upgraded to v5.0.0

Feature/Dependency Upgrade. (#1)

* Domain model upgraded to v4.0.0.
* Criteria upgraded to v4.0.0.
* Dropped support for PHP 8.1.

Feature/Added Criteria package.