Function payload_accept_header_value 

pub fn payload_accept_header_value(types: &[&str]) -> String

The PAYLOAD_ACCEPT_HEADER value for types, the way parse_payload_accept reads it back.

use cratestack_core::payload_accept_header_value;

assert_eq!(
    payload_accept_header_value(&["application/json", "application/cbor"]),
    "application/json, application/cbor"
);