Add support for with_request_body in SecurityPolicy.spec.extAuth

[mjf-89]

Envoy supports sending the full request body to the external authorization server via the with_request_body filter configuration. Do you think that it is possible to expose such feature on the SecurityPolicy.spec.extAuth api?

My use case specifically relates to LLM model serving with an OpenAI compatible server. There you receive a request JSON body with a model field. I would like to have an opa-envoy authz server that is able to authorize requests based on the user identity and the model requested.

Relevant Links:

• https://www.envoyproxy.io/docs/envoy/latest/configuration/http/http_filters/ext_authz_filter#configuration-examples