Is your feature request related to a problem or challenge?

Someone asked in discord:

I'm looking at Datafusion and Polars as potential solutions for calculating averages over a sliding window of events, where the window is bound by event time. I've just come across Datafusion, would anyone be able to clarify if it's suitable for this use case? In essence, I have events streaming in via RPC that I want to feed into a a system that gives the above outcome.

I am pretty sure this is exactly the case for using UNBOUNDED tables with explicitly defined ORDER BY from Synnada and Arroyo others. However, when I went to look for the documentation, I could't find any mention of this usecase or documentation of unbounded tables

Describe the solution you'd like

I would like to help make it easier for people to use DataFusion for streaming usecases by:

• Documenting the UNBOUNDED keyword in the CREATE EXTERNAL TABLE documentation
• Add an example in https://github.com/apache/arrow-datafusion/tree/main/datafusion-examples/examples with a simple streaming example (perhaps implementing some simple version of the use case described in the description)
• Add a section to the library guide giving some basic overview

Describe alternatives you've considered

No response

Additional context

No response