feat: impl GetSchema in ADO.NET

[KirillKurdyukov]

https://learn.microsoft.com/en-us/dotnet/framework/data/adonet/common-schema-collections

[Pankraty]

Hi! Are there any plans for adding GetSchemaTable too? I am looking for capability to fetch information about table columns, and it seems, this might be the way for me. Other possiblilities are basically closed as the classes describing schema are mostly internal.