Introduce synchronize_fork feature flag

Igor Drozdovrequested to merge
id-feature-flag-for-sync-fork into master

What does this MR do and why?

The functionality has been released behind fork_divergence_counts feature flag.

But we can benefit from a separate feature flag, for example, in the cases, when divergence counts work as expected while synchronization has issues.

MR: !106575 (merged)

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