Allow `DbType` to do type conversions

[Jolanrensen]

Currently, you can only specify how the JDBC types are mapped to a KType/ColumnSchema.
This must strictly follow the types of the specific implementation of the DataBase JDBC integration to prevent runtime errors, often resulting in very non-Kotlinlike types, such as java.sql.Date, DuckDBBlobResult, or org.duckdb.JsonNode.

Other DataFrame integrations aim to convert the types to something close to kotlin, such as KotlinX LocalDateTime.
Allowing to specify a conversion like this would also allow conversions like SomeJsonFormat -> ColumnGroup/FrameColumn on-the-fly #462 and java.sql.Array -> List<T>