Add String and FixedString Key Support for sumMap

Why it matters

This feature enables users to use sumMap with string-based keys, allowing aggregation of map data where keys are strings or fixed-length strings. It expands the versatility of the sumMap function beyond numeric keys, solving limitations in handling categorical or textual keys.

How to use it

Users can now pass columns with String or FixedString types as keys to the sumMap aggregate function in their queries without any additional configuration.