Package application documents patterns for building Controllers to manage specific applications.
An application is a Controller and Resource that together implement the operational logic for an application. They are often used to take off-the-shelf OSS applications, and make them Kubernetes native.
A typical application Controller may use builder.ControllerManagedBy() to create a Controller for a single API type that manages other objects it creates.
Application Controllers are most useful for stateful applications such as Cassandra, Etcd and MySQL which contain operation logic for sharding, backup and restore, upgrade / downgrade, etc.