Painless docs: Update datetime examples to use same dataset

The refreshed Painless docs include a section "Datetime examples in contexts". The updated docs aren't yet merged but I expect the page will appear at: https://www.elastic.co/docs/reference/scripting-languages/painless/painless-datetime-examples-in-contexts

As [requested here](https://github.com/elastic/elasticsearch/pull/137211/files#r2683727366), the examples require loading a set of data. Perhaps the examples could be updated to use the same eCommerce data set that we're using for all other examples in the Painless docs.

I'm not sure if the eCommerce data set lends itself to datetime examples, but I'm opening this for exploring since we had the request.