Add test for downloading ingested file

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Description

currently the tests to verify-doa and verify-download from #100 only verify the endpoint responds with 404.
e.g. https://github.com/neicnordic/sda-helm/blob/master/charts/sda-svc/test/verify-doa.py

DoD

We would need to test that a file can be downloaded, and we would need:

• mock oidc - we could use from https://github.com/neicnordic/sda-download/tree/main/dev_utils/mockoidc
• verify doa and download endpoints that datasets can be retrieved with token generated by mock oidc as well as files can be retrieved

Testing

e2e added