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Operators who have never overridden the broker config (i.e., it is implicitly `500`) need no action.

Test Plan

Unit Tests

ShareCoordinatorConfigTest (covers the broker-level bounds change)

ShareCoordinatorShardTest (covers the per-group config)

GroupConfigTest (covers the runtime use of the per-group value)

Integration Tests

 ShareCoordinatorIntegrationTest (covers end-to-end propagation of the per-group config) - Extend ShareCoordinatorConfigTest, ShareCoordinatorShardTest and GroupConfigTestIntegration Tests - Extend ShareCoordinatorIntegrationTest

Rejected Alternatives

Here are the rejected alternatives.

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