Rework the phenotype severity heatmap figure

[bschilder]

• [x] Switch from high/medium/low severity to use the Profund/Severe/Moderate/Mild categories introduced here: #4
• [x] Split the plot into two column-wise facets: Congenital phenotypes (always/often) vs. Non-congenital phenotypes (never/rarely)

Current version

Link to the last commit before makes the changes below (in case we need to switch back at some point): https://github.com/neurogenomics/gpt_hpo_annotations/blob/8dbf16c99bd5ed020b6f6bfa9e50b316fd87ead1/manuscript.qmd#L394

[bschilder]

New version