v1.50.4

Bug fixes and other changes

• Remove version number from default version comment
• remove remaining instances of python-dateutil pin
• upgrade boto3 and remove python-dateutil pin

Documentation changes

• Add issue templates and configure issue template chooser
• Update error type in delete_endpoint docstring
• add version requirement for using "requirements.txt" when serving an MXNet model
• update container dependency versions for MXNet and PyTorch
• Update supported versions of PyTorch