[API-7827]: Stop using url parameters to authenticate Score API requests

[esingin-sift]

Purpose

• Stop using url parameters to authenticate Score API requests
• https://sift.atlassian.net/browse/API-7827

Summary

Call Sift endpoints with Basic Authentication instead of sending api_key as a request parameter.
Applied to the following calls:
Anthropic raised a concern about our sift-python SDK logging api keys when an exception occurs. This affects these calls:

• Score (client.score() in sift-python)
• Get Score (client.get_user_score() )
• Rescore User (client.rescore_user())
• Unlabel (client.unlabel())

Testing

• Unit Tests
• Integration testing app

Checklist

• The change was thoroughly tested manually
• The change was covered with unit tests
• The change was tested with real API calls (if applicable)
• Necessary changes were made in the integration tests (if applicable)
• New functionality is reflected in README

[sbogolii-sift]

LGTM