Serverless: AI Gateway support

## Jobs to be done (optional)

## Definition of done
- mention that serverless is an option here: https://developer.konghq.com/ai-gateway/#ai-gateway-in-konnect , https://developer.konghq.com/serverless-gateways/ , https://developer.konghq.com/serverless-gateways/reference/
- Managed cache, this isn't supported, correct?
- How to on a use case (AI prototype?) and include set up and securing steps (https://developer.konghq.com/serverless-gateways/reference/#securing-backend-communication)

## Information
PRD: https://docs.google.com/document/d/1_M_FSlAqSUvpa6ItoMa_VD0dunmgpg0UPYflzIsYf8Q/edit?tab=t.cgvgfo56gkrr#heading=h.6mpt4rldoyrf
Aha: https://konghq.aha.io/epics/CGW-E-49

## Due date (optional)

## Size

Start by reviewing the linked AI Gateway and serverless gateway documentation, especially the securing-backend-communication section, and clarify whether managed cache is supported. Done means the AI Gateway page mentions serverless, the relevant serverless pages are updated, and a use-case how-to covers setup and securing backend communication.

Written by the indexing model from the issue text.