Optimize boxplot right margin

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After rotating boxplot x-axis labels 45 degrees, as suggested by @dunnpa, some right side labels are truncated by default right margin. To include all x-axis labels in the plot, the right margin is set with the following procedure. However, this procedure needs to be optimized for the following two purposes:

• Guarantee that all x-axis labels are included and not truncated.
• Guarantee that right margin always extend the rightmost label by 5.5 points, which is the default ggplot2 margin.

https://github.com/PediatricOpenTargets/OpenPedCan-api/blob/b265d7b74028c5d2dc126cea69cf043fe740ad7d/src/get_gene_tpm_boxplot.R#L75-L87

Example boxplot with truncated x-axis labels:

library(ggplot2)
data(diamonds)
diamonds$cut <- paste("Very very very long x-axis labels like our boxplot",as.character(diamonds$cut))
qplot(cut,carat,data=diamonds,geom="boxplot") +
  theme(axis.text.x = element_text(angle = -45, vjust = 1, hjust = 0))