Add Trino 468 release notes

docs/src/main/sphinx/release.md

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+release/release-468
 release/release-467
 release/release-466
 release/release-465

docs/src/main/sphinx/release/release-468.md

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+# Release 468 (11 Dec 2024)
+
+## General
+
+* Add experimental support for Python user-defined functions. ({issue}`24378`)
+
+## Hive connector
+
+* Deactivate bucket execution when not useful in query processing. ({issue}`23432`)
+* Enable mismatched bucket execution optimization by default. This can be
+  disabled with `hive.optimize-mismatched-bucket-count` configuration property,
+  and the `optimize_mismatched_bucket_count` session property. ({issue}`23432`)
+
+## Iceberg connector
+
+* Add bucketed execution to improve performance when running a join or
+  aggregation on a bucketed table. This can be deactivated with
+  `iceberg.bucket-execution` configuration property, and the
+  `bucket_execution_enabled` session property. ({issue}`23432`)
+* Deprecate the `iceberg.materialized-views.storage-schema` configuration
+  property. ({issue}`24398`)  
+* {{breaking}} Rename the `partitions` column in the `$manifests` metadata table
+  to `partition_summaries`. ({issue}`24103`)
+
+## PostgreSQL connector
+
+* Add non-transactional support for [MERGE statements](/sql/merge). ({issue}`23034`)
+
+## SPI
+
+* Add partitioning push down, which a connector can use to activate optional
+  partitioning, or choose between multiple partitioning strategies. ({issue}`23432`)