fix: Degreed: Missing Learner Data Audit Records

[johnnagro]

Description

• degreed2 seems to be unable to successfully send learner audit records
• looks like we were serializing data in the client rather than the model
• integrated channel transmitter was expecing serialization in model
• test tweaks but there is more we can add to tests

Associated Splunk logs:

2022-03-09 14:59:48,232 ERROR 1450 [celery.app.trace] [user None] [ip None] trace.py:265 - Task integrated_channels.integrated_channel.tasks.transmit_learner_data[f5628262-9285-4ad3-864a-6d958cc8e920] raised unexpected: AttributeError("'Degreed2LearnerDataTransmissionAudit' object has no attribute 'serialize'")
Traceback (most recent call last):
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/celery/app/trace.py", line 451, in trace_task
    R = retval = fun(*args, **kwargs)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/newrelic/hooks/application_celery.py", line 99, in wrapper
    return wrapped(*args, **kwargs)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/celery/app/trace.py", line 734, in __protected_call__
    return self.run(*args, **kwargs)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/edx_django_utils/monitoring/internal/code_owner/utils.py", line 193, in new_function
    return wrapped_function(*args, **kwargs)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/integrated_channels/integrated_channel/tasks.py", line 109, in transmit_learner_data
    integrated_channel.transmit_learner_data(api_user)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/integrated_channels/integrated_channel/models.py", line 197, in transmit_learner_data
    transmitter.transmit(exporter)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/integrated_channels/degreed2/transmitters/learner_data.py", line 35, in transmit
    super().transmit(payload, **kwargs)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/integrated_channels/integrated_channel/transmitters/learner_data.py", line 260, in transmit
    serialized_payload = learner_data.serialize(enterprise_configuration=self.enterprise_configuration)
AttributeError: 'Degreed2LearnerDataTransmissionAudit' object has no attribute 'serialize'

References

• ENT-5558

[binodpant]

lgtm, we don't have a staging env to test sgainst rn we will have to test in prd for now until we have integ testing setup (discussed offline)