ggplot2-在图形区域之外绘制线条并注释文本

Question

我有以下数据：

fixed <- as.data.frame(rep(0.125,8))
fixed[,2] <- c("1","2","3","4","5","6","7","8")
colnames(fixed) <- c("Percentage", "Test")

并生成以下图形：

现在我要实现这样的目标。但是，我还没有找到一种在图形区域之外绘制并编写单独的轴标签的方法。那可能吗？

我的情节代码在这里：

p <- ggplot(fixed,aes(x=Test ,y=Percentage,fill=Test))+
  geom_boxplot()+ 
  stat_summary(fun.data = function(y) 
    data.frame(y=0.6, label = paste(round(mean(y),2))), geom="text",size=3) +
  geom_hline(yintercept=0.55, linetype="dashed", color = "black")+
  theme(legend.position="none")+
  scale_y_continuous(limits = c(0, 0.6),breaks=seq(0,0.6,0.1),
                     labels= c("0%","10%","20%","30%","40%","50%","Mean"))+
  theme_bw()+
  labs(title = "Title")+
  xlab("Test")+
  ylab("Percetage")+
  theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank(),
        panel.background = element_rect(fill = "grey90", colour = NA),
        plot.background = element_rect(fill = "grey90", colour = NA),
        legend.position="none",plot.title = element_text(size= 12, hjust=0.5),
        plot.margin = unit(c(1,1,1,1), "cm"))+
  scale_fill_manual(values=c("#00441b","#006d2c","#238b45","#41ab5d","#74c476",
                             "#a1d99b","#c7e9c0","#e5f5e0"))
p