Analyze webpack compilation stats for performance insights

We save our webpack compile stats for every CI pipeline's gitlab:assets:compile job within a stats.json file. This file contains all the information we need to identify key metrics that we can use to improve the performance of GitLab, including:

• Average/median/mean entry point sizes (lower is better)
• Max entry point size. List of the largest and most problematic ones.
• Average number of chunks per module (lower is better, ideal is 1 chunk per module)
• Max number of chunks per a single module. List modules that appear in multiple chunks, sorted by size
• Total webpack build time and max heap size.

Deliverable

• Create means to calculate the metrics above from our stats.json output.
• Prescribe goals to improve each of these metrics over time, and document "ideal" values within our frontend guidelines.