Decouple Kinto Setup From Client Scenarios in Merino Contract Tests

[data-sync-user]

In order to facilitate adding contract test cases, add functionality to define which suggestion data should be setup for kinto per scenario. The current contract test design will load, via kinto-setup, all data found under directory volumes/kinto. Adding this form of flexibility will prevent older tests from breaking when new functionality is added.

This could perhaps be accomplished at the file level, having different client scenarios.yml files paired with kinto data files or perhaps it could be defined as part of the scenarios themselves.

┆Issue is synchronized with this Jira Task
┆epic: Develop contract tests for suggestion data changes in RS