I need the way to get a user the opportunity to set the columns headers. Moreover, the columns headers should be saved separately from the main spreadsheet data.

Of course, the possible variant is to have two spreadsheets: the one – for the data, the second (with one row) – for the headers.

But the better way is to get a user the opportunity to set the spreadsheet columns headers.
It would be ideally if a user could change “A”, “B”, “C” for “ID”, “Product”, “Quantity” …
Not to have a first row for headers, but change the spreadsheet columns headers!
Moreover, we have the context menu on the columns headers and it is possible to add one more item “Edit” in it.