[Improvement] Add `Unknown` column data type to handle an unresolvable type from the catalog

[mchades]

What would you like to be improved?

If a column data type in the catalog does not have a mapping in Gravitino, an exception will be thrown.

Ideally, we should map all data types from a catalog to Gravitino. However, in practical situations, loading exceptions may occur due to the addition of new data types or insufficient mapping support.

How should we improve?

Add an Unknown column data type to handle an unresolvable type from the catalog, to ensure the table load successfully

[FANNG1]

+1, loadTable is import for the newbies to try Gravitino

[SteNicholas]

@mchades, could you assign this ticket to me? Thanks.

[FANNG1]

@jerryshao , what do you think to introducing Unknown Type?

[jerryshao]

If it is a unknown type, how would user know the actual type of the underlying sources? I would suggest to treat like a unparsed/unresolved type like what we do for unparsed expression, WDYT?

[FANNG1]

@SteNicholas can we use a UnparsedType like UnparsedExpression with a field to describe underlying types?

[SteNicholas]

@SteNicholas can we use a UnparsedType like UnparsedExpression with a field to describe underlying types?

@FANNG1, I will update the pull request to use UnparsedType. cc @mchades