[MSUE-157] - Support Score Percentiles in response

[haneeshv]

Purpose

Support score percentiles in sift-php

Summary

In our REST API we support the fields GET-param where we can specify some extra fields that will be populated in the response. SCORE_PERCENTILES is one of them and we need to add support of it in the client library

Testing

Example of the Events API call using percentiles - https://api.sift.com/v205/events?fields=SCORE_PERCENTILES

Checklist

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