Ability to define metadata (possible columns) for Tabular data source

[yecli]

As we introduced Tabular data sources (with tabular converters), we need to add metadata that could be used to manage resulting tabular file columns structure.
So we need to have an ability to add metadata that is specific to converted tabular object.

Registering tabular metadata could be done using WithTabluarMetadata method on data source registration. This will fill TabularMetadata property on ExporedTypeDefinition. ExportMetadata.GetFromType could be used here for initial filling;

Based on provider selection, tabular on non-tabular set of columns should be shown when selecting columns.
Provider selector should be placed first (even before selecting exported type), as it could change "Exported types" available types and "Select columns" available columns.