Add kapa.ai widget

[jeffreyad]

Add kapa.ai widget like was done for admiral pharmaverse/admiral#2890

https://docs.kapa.ai/kapa-for-open-source

[bms63]

@manciniedoardo do you think they will give us another instance to use for the examples site?

this would be more interesting as there are more packages and IGs to cite

[manciniedoardo]

I think we can ask!

[rossfarrugia]

@manciniedoardo will discuss this with you at our next call - the examples team all agreed today at our meet that this would be a great idea!