@Nullable
    public static CallOptions get(RequestContext ctx) {
        requireNonNull(ctx, "ctx");
        return ctx.attr(GRPC_CALL_OPTIONS);
    }
Returns {@link CallOptions} which was set to the specified {@link RequestContext} using
{@link #set(RequestContext, CallOptions)}.
grpc/src/main/java/com/linecorp/armeria/common/grpc/GrpcCallOptions.java