When creating an external catalog, Doris will automatically sync the schema of table from external catalog.
But some of column type are not supported by Doris now, such as struct, map, etc.
In previous, when meeting these unsupported column, Doris will throw an exception, and the corresponding
table can not be synced. But user may just want to query other supported columns.
In this PR, I add a new column type: UNSUPPORTED. And now it is just used for external table schema sync.
When meeting unsupported column, it will be synced as column with UNSUPPORTED type.
When query this table, there are serval situation:
select * from table: throw error Unsupported type 'UNSUPPORTED_TYPE' xxx
select k1 from table: k1 is with supported type. query OK.
select * except(k2): k2 is with unsupported type. query OK
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