Add color function

[DanyangDai]

Hello

I have tried to add the color options to allow for different colors for groups of geom_points and the errorbars. I had difficulty to make the alinement of the table rows and geom_points after adding the color legend at the bottom of the forest plot.

You can have a look at what I've tried from: master...DanyangDai:forester:master

I think the difficult part is to adjust for the patchwork with the additional color legend at the bottom of the plot. This current patchwork::inset_element(center, align_to = "full", left = (left_width/total_width), right = ((ggplot_width + left_width)/total_width), top = 0.97, bottom = 0)
works for my forestplot setting but it does need adjustment to makesure the alinement for the table rows and geom_point and errorbars based on the number of table rows.

Hope people know more about patchwork would assist on the alinement with color legend at the bottom.

Thanks!