chore: add changelog entry

Co-Authored-By: Zaiming (Stone) Shi <zmstone@gmail.com>

changes/ce/feat-11935.en.md

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+Switch to the new `v2` routing store schema by default. New schema improves both subscription and routing performance, especially so for scenarios with concurrent subscriptions to topic filters sharing common wildcard prefixes, at the cost of slightly increased memory usage. This schema also eliminates the need for a separate index, thus inconsistencies in the routing state rarely encountered in previous versions should no longer be possible.
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+If a cluster is rolling upgraded from older version, the cluster will continue to use `v1` store until a full cluster (non-rolling) restart happens.
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+The former schema can still be forced by setting `broker.routing.storage_schema` configuration option to `v1` and conducting full non-rolling cluster restart as well.