make oauth-proxy send audit ID with its requests

OAuth-Proxy should send an Audit-Id header with its requests to the kube-apiserver so that we can easily track its requests and be able to tell which arrived and which were processed.

This comes from a time when the CI was in disarray and oauth-proxy requests were failing to reach the KAS but we did not know if at least any were processed or if they were just all plainly rejected somewhere in the middle.