Update image.R to enable control of image file size

[solvi808]

Added the parameters absolute_height and dpi to ggplot_image() in order to enable precise control of the saved image quality and absolute size, passed to ggsave()

Summary

Following my discussion at https://github.com/rstudio/gt/discussions/1482 I have made a quick fix to solve this issue

Related GitHub Issues and PRs

- Ref: #

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