The alloydb_scann extension is updated to include the following vector search improvements in Preview

## Announcement The `alloydb_scann` extension is updated to include the following vector search improvements in [Preview](https://cloud.google.com/products#product-launch-stages): * AlloyDB for PostgreSQL introduces inline filtering for vector search. With inline filtering, SQL filter evaluation is performed at the same time as vector search. This feature mitigates potential issues from existing pre and post-filter evaluation mechanisms. For more information about `scann.enable_inline_filtering`, see [ScaNN index reference](https://cloud.google.com/alloydb/docs/reference/ai/scann-index-reference). * A distribution histogram is available in the `pg_stat_ann_indexes` view, which helps you understand the distribution of vectors between partitions and `num_leaves` of your ScaNN index. For more information, including recommendations about tuning the `distributionpercentile` metric, see [Tuning metrics](https://cloud.google.com/alloydb/docs/reference/vector-index-metrics#tuning-metrics).