Kapa: Vertex audio models

## Jobs to be done (optional)

From this issue: https://app.kapa.ai/93b55f65-cffb-4d0b-9da7-c8915a838dce/conversations/f3f03532-8cc2-4804-81b6-ea9ac8960f45

- We don't list any audio under https://developer.konghq.com/ai-gateway/ai-providers/vertex/#supported-capabilities for the provider
- The proxy can handle audio https://developer.konghq.com/plugins/ai-proxy/examples/audio-translation-openai/
- Confirm the capabilities list is up to date
- Harden the language of capabilities sections across all providers to highlight this is exhaustive

## Definition of done

- Identify if the capability exists
- add capability or add stronger language

## Size

- M (Medium) Example: writing a UI how to for a straightforward product, adding a plugin example