Add support for row_number()

[hongooi73]

[alexkyllo]

There's a good workaround for this, you can express it using the Kusto syntax within a mutate expression

mutate(rn = row_number(1, prev(group) != group))

gets translated to

| extend ['rn'] = row_number(1, prev(['group']) != ['group'])

You just have to make sure to do this after an arrange call because row_number in Kusto only works on sorted data.