private static String joinAllowedRequestHeaders(CorsPolicy corsPolicy) {
        return joinHeaders(corsPolicy.allowedRequestHeaders());
    }
Joins the set of allowed request headers into a single string.
This method utilizes {@link #joinHeaders(Set)}
to create a comma-separated list of allowed request headers.

@return A {@link String} representing the joined allowed request headers.
core/src/main/java/com/linecorp/armeria/internal/server/CorsHeaderUtil.java