Custom headers are not available to the SNI `override_auto_sni_header` when added using `request_headers_to_add`

Title

Custom headers are not available to the SNI override_auto_sni_header when added using request_headers_to_add

Description

We now allow a customer header to populate the SNI for the upstream requests [Link]. But, if the custom header is not coming from downstream and gets added anywhere using request_headers_to_add then it's value is not available here as this piece of code to populate the SNI gets invoked before we add/modify the request headers probably here.