Track webpack performance metrics over time and warn users via CI jobs

After #34097 (closed) is completed, we need to take our webpack goals a CI-based warning system to prevent users from inadvertently harming performance with their changes.

Warnings should be generated along the lines of:

The changes in this branch increase the entrypoint size of the projects:show action by 22%. Have you considered using code-splitting to reduce user TTI for this page?

or

The changes introduced in this branch cause the pdf.js module to be duplicated across three chunks. Please take care to ensure large vendor libraries are not duplicated in GitLab's codebase