Allow non matching schemas on export partition

[arthurpassos]

1. A source table with more columns should be exportable to a destination with less columns
2. Compatible data types should be accepeted even if it is not a 100% match (e.g, int32 -> int64. This does not apply to int64 -> int32)

[arthurpassos]

The 2nd item is implemented by #1779, tho we do allow lossy casts because we need them.

1st is still not implemented