Documentation on use case for Extender resource

[kachawla]

What content needs to be created or modified?

We often get questions on using recipes for technologies that do not have first class support through a portable resource category yet - Extender resource is supposed to fill this gap currently. However our documentation on recipes does not have any mention of Extender resource type and pointing user in the right direction if existing portable resource types do not fit their use case. The only documentation we have on Extender is nested in the resource schema and the list of supported resources, so it is not easily discoverable either.

Describe the solution you'd like

Add an explicit note on the Recipes overview page about when to use an extender resource.

Where should the new material be placed?

https://docs.radapp.io/guides/recipes/overview/

The associated pull request from the Radius code repo, if applicable

n/a

Additional context

AB#11766