public static void corsHeadersSet(ServiceRequestContext ctx) {
        ctx.setAttr(IS_CORS_SET, true);
    }
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