Fix custom_objects for regularizers and other issues (#5012)
Fix custom_objects for regularizers and other issues (#5012)

* Fix custom_objects for regularizers and other issues

* Add custom_object_scope

* Update optimizers and Lambda to respect global_custom_objects

* Add generic_utils to mkdocs and add tests for custom_object_scope

* Fix elif statement in optimizers.py

* Clean up generic_utils.py docstrings

keras-team/keras-autodoc