ENH: add plot-feature-volatility to maturity-index pipeline

[nbokulich]

Improvement Description
maturity-index produces feature importances, so plot-feature-volatility could be another interesting way to visualize the feature data, and be another place to show off those feature volatility plots...

Current Behavior
Right now longitudinal feature abundances are shown in a heatmap, which is a better overview, but has its weaknesses. Generate both visualizations? Or consider replacing heatmaps?

Proposed Behavior
add plot-feature-volatility to the pipeline! This would (could but really should) require adding individual_id_column as a parameter.

Questions

1. Replace the heatmaps or not? The heatmaps are a great overview, but are slow and do not show per-individual volatility.