Added initializeAggregation function for single value initialization

Why it matters

This feature allows users to create an aggregation state starting from one value instead of incrementally aggregating multiple rows. It simplifies scenarios where a known initial aggregation state is needed, enhancing flexibility in data processing and aggregation logic.

How to use it

Use the initializeAggregation function by passing a single value to initialize the aggregation state. This can be applied in queries wherever you need to start aggregations from a specific value rather than aggregating over multiple rows.