Move duo_workflow_service/client.py to scripts/test_client.py

Problem

Currently, the test client is located under duo_workflow_service package namespace. This should be moved to the other place in order to make it clear that it's for a testing purpose.

Proposal

Move duo_workflow_service/client.py to scripts/test_client.py.

Auto generated

The following discussion from !12 (merged) should be addressed:

• @ottilia_westerlund started a discussion: (+3 comments)

  Is there a specific reason we use grpc.insecure_channel without ChannelCredentials here?