Finalizers allow a reconciler to clean up state for a resource that has
been deleted by a client, and not yet fully removed. Resources with
finalizers will stay in this terminating state until all finalizers are
cleared from the resource.

ParentReconcilers will now reconcile resources that are terminating as
long as they also have a pending finalizer.

SyncReconcilers have a new, optional, Finalize method that is called
when the resource is terminating. The Sync method will not be called
unless SyncDuringFinalization is true. Users are responsible to add and
clear finalizers from resources.

The AddParentFinalizer and ClearParentFinalizer functions will patch the
resource. These method work with cast parents objects and use the same
client the ParentReconciler used to originally load the parent resource,
so they can be called inside SubReconcilers that use a different client.

ChildReconcilers have a Finalizer field that when set will ensure that
value is set on the parent resource finalizers before creating/updating
a child resource. It will also clear that finalizer after the child is
deleted. When the parent is terminating, the DesiredChild method is not
called and existing children are deleted.

Signed-off-by: Scott Andrews <andrewssc@vmware.com>

Signed-off-by: Scott Andrews <andrewssc@vmware.com>

Co-authored-by: Max Brauer <mamachanko@users.noreply.github.com>