fix: Update DataSystemConfig to accept list of synchronizers

[keelerm84]

Note

Medium Risk
Changes core data-source failover/recovery logic in FDv2, which can affect initialization and update behavior under network failures, though it is covered by updated unit/contract tests.

Overview
Extends Data System synchronization configuration from a fixed primary/secondary model to an ordered list of synchronizers. DataSystemConfig and ConfigBuilder.synchronizers() now accept multiple synchronizer builders (with validation for empty input), and contract-test config parsing is updated to build this list.

FDv2’s synchronizer loop is refactored to iterate/fail over the list (including recovery to the first choice), with an explicit ConditionDirective to differentiate fallback vs recover vs continue decisions; tests are updated/expanded accordingly. CI contract tests are also bumped to v3.0.0-alpha.3 and YAML quoting is normalized.

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[jsonbailey]

I added a suggestion but don't consider it a blocker.

[jsonbailey]

In Ruby I ended up collapsing this down to a single result, essentially adding the remove sync and fallback as options of the Conditional Directive. From my understanding they are all independent of each other. If you have fallback, you don't care about the other two, if you have remove sync, you don't care about the conditional directive, so there isn't a need to have all three returned.