timestamp required to instantiate files

[thclark]

Bug report

What is the current behavior?

A timestamp is required to instantiate Datafiles

What is the expected behavior?

If data files don't have a timestamp naturally associated with them, they should be able to be instantiated without one.

Your environment

• Library Version: 0.1.17
• Platform MacOS | Windows | Linux | Other

Other information

    def save(self, *args, **kwargs):
        """ Override the save method to synchronize metadata to the cloud store
        """
        meta = self.get_instance_metadata()
        tags = list(f"{k}:{v}" for k, v in meta.items())
        # Make a DUMMY datafile (path may or may not be correct) used solely as a serialisation helper for the metadata
>       df = Datafile(id=self.id, path=self._file_field.name, tags=tags)
E       TypeError: __init__() missing 1 required positional argument: 'timestamp'

=================================================================================================== short test summary info ====================================================================================================
FAILED backend/test/datalake/test_datalake.py::DatalakeTestCase::test_creation_with_meta - TypeError: __init__() missing 1 required positional argument: 'timestamp'

root@6dd4ad891cb2:/app# pip show octue
Name: octue
Version: 0.1.17
Summary: A package providing template applications for data services, and a python SDK to the Octue API
Home-page: https://www.github.com/octue/octue-sdk-python
Author: Thomas Clark (github: thclark)
Author-email: support@octue.com
License: MIT
Location: /usr/local/lib/python3.8/site-packages
Requires: Flask, google-cloud-pubsub, google-crc32c, google-cloud-storage, click, coolname, gunicorn, twined, google-cloud-secret-manager
Required-by: 
root@6dd4ad891cb2:/app#