[improve]: `create_materialized_view_w_flattened_json_column`: column duplication management

[ArturoDiez]

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I found great use to the create_materialized_view_w_flattened_json_column function, really straightforward and useful to manage JSONs in BQ.

I came with an issue tho, there were some table that I would have duplicated columns, because one column that was in the initial table was also at the first nest level of the JSON with the first name (generally the same data also, so deleting one of them was the objective). It would be really nice if there was any way to manage it, since managing the flattened_json_column function directly is kinda tricky.