Missing operation description for the "composite" operation prevents its use in CLI

When the "composite" operation registration was converted to OperationDefinition, the outputting of the operation description was lost. This is because the operation is registered as EntryType.PRIVATE and we don't produce descriptions for those operations. Without such a description, any attempt to use the low-level op directly via the CLI will fail:

[standalone@localhost:9999 /] /:composite(steps=[

])
Operation 'composite' does not expect any property.

See WFLY-1315 for the task of perhaps making this operation EntryType.PUBLIC.

The task here is to hack in something so a description gets published even though the operation is EntryType.PRIVATE. This is a conservative approach to restore the behavior we had in EAP 6.0.x and can be backported to EAP 6.1.0.