fix: Expand data system config to allow for list of synchronizers

[keelerm84]

Note

Medium Risk
Changes core data-source failover behavior and configuration surface area; regressions could affect client initialization and data freshness during outages.

Overview
Updates the FDv2 data system to support an ordered list of synchronizers instead of a fixed primary/secondary pair, with runtime logic to fall back to the next synchronizer, recover back to the first when healthy, and permanently remove synchronizers that fail/return Off.

Refactors configuration APIs and structs (DataSystemConfigurationBuilder.Synchronizers, SynchronizersConfiguration) and updates the contract-test service config schema to accept synchronizers as a list; FDv1 fallback is now triggered only when a synchronizer explicitly requests RevertToFDv1.

Updates end-to-end tests to match the new warning/log behavior and bumps CI contract test v3 to v3.0.0-alpha.3.

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