workflows: new name for ObjectVersion
- Renames ObjectVersion FINAL to COMPLETED for consistency with engine states and mid-level-API naming.
- Sets DeprecationWarning on COMPLETED via new helper function.
- Introduces staticproperty and classproperty decorators.
Reviewed-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
Signed-off-by: Dimitrios Semitsoglou-Tsiapos <dsemitso@cern.ch>