Update - adding `row_number` function

[amyshwang]

Describe the requested changes:

In the core repo QuestDB has row_number() function that is not yet documented.

The task involves: Create a new section for the function, following the template. Provide useful example(s) to explain how to use it in QuestDB.

Location: A new section in https://questdb.io/docs/reference/function/aggregation/

[Smartmind12]

Hey Could you assign this issue to me as i would like to work on it...Thanks!

[TiwariAbhishek23]

I want to contribute to this one, please assign

[amyshwang]

@AbhishekTiwari23 sorry - first come first serve - this is assigned to @Smartmind12. We have other tasks and you're more than welcome to pick another one!