Add custom headers using Svix.message.create along with payload , event type

[PurvaSatish]

https://api.svix.com/docs#tag/Message/operation/v1.message.create
Can we have a parameter to add custom headers in svix, I have an endpoint which gives me an auth token and must be sent as header with the endpoint created by svix. we do not want to use the auth token provided by svix.

[svix-jplatte]

This is the same as #1494, right?