Add support for adding extra headers sent to ext auth based on different requests.

*Description*:
Our case needs to add some extra req headers to ext auth service,but not for all requests,besides,we may need to add differenet headers based on different requests.I've tried Client Traffic Policy like https://github.com/envoyproxy/gateway/issues/4267, but the policy can only refer to gateway,so it affects all requests,I wonder if there are any more fine-grained configurations? Thanks.

[optional *Relevant Links*:]
(https://github.com/envoyproxy/gateway/issues/4267)