Add 4.6.18 release notes

Author: kriszyp

release-notes/v4-tucker/4.6.18.md

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+---
+title: 4.6.18
+---
+
+### HarperDB 4.6.18
+
+11/21/2025
+
+- Reduced frequency of unnecessary `end_txn` messages that were causing excess traffic from node without originating writes.
+- Fix to allow `databases` config in replication support a database name as a string or an object
+- Backport fix for ensuring that we don't failover connections (when failover is disabled) when re-connections take place.
+- Update last received status when receiving sequence id updates for better reporting of cluster status