Configure trusted proxy auth during setup

Upserts trusted proxy settings for remote trusted-proxy mode, including the expected initial owner email.

curl -X POST "https://example.com/v1/setup/trusted-proxy/configure" \  -H "Content-Type: application/json" \  -d '{}'

{  "configured_at": 0,  "has_shared_secret": true,  "session_expires_at": 0,  "setup_owner_email": "string",  "state": "uninitialized"}