Unify adit-client usage examples

[andreweuw]

There are inconsistent examples of how to use adit-client across the project, for example:

• Correct one at https://github.com/openradx/adit/tree/main/adit-client#code

client = AditClient(server_url, auth_token)
studies = client.search_for_studies("ORTHANC1", {"PatientName": "Doe, John"})

• Altered one at https://github.com/openradx/adit/blob/main/docs/user-docs/admin-guide.md#adit-client

client = AditClient(base_url, token)
studies = client.search_studies(patient_id="12345")

• Combining the correct and the altered one at Add NIfTI conversion API #300 at API Usage (adit-client) example

client = AditClient(server_url, token)