Skip null subcolumns of ephemeral columns

[BentsiLeviav]

Describe the bug

The connector skips ephemeral columns during table description but still processes their .null subcolumns, causing errors like:

Got non-root column, but its parent was not found to be updated. UINT8{name=some_ephemeral_column.null}

• The connector skips ephemeral columns in describeTableV1 and describeTableV2
• However, it doesn't skip the subcolumns related to those columns (for instance, .null)

Expected behaviour

Skip both ephemeral columns and their subcolumns during table description (with no errors)

[ne1r0n]

The issue is very similar to #519

[chernser]

This message is actually a warning. We have lowered log level and will fix it along with schema validation.