Add support for experimental Variant data type

[mshustov]

[The type is experimental]. See the docs https://clickhouse.com/docs/en/sql-reference/data-types/variant There will be more added for better support of the semistructured data https://github.com/ClickHouse/ClickHouse/issues/54864

[Gictorbit]

I also have this error when using Variant:

assertion failed: error is not nil: clickhouse: unsupported column type "Variant(Bool, Float64, String, UInt64)"