Add GitHub Actions for tracking changes in sizes to packages

We want to ensure that the packages we ship are as minimal as possible so that we don't unnecessarily bloat the apps that are using these packages.

To do this, we should track how large each package is when installed, and we should add a GitHub Action which automatically posts a comment on new PRs and reports the sizes of packages affected and a measure of how those sizes have changed (both using bytes and also percentages). We should store this information in artifacts which can later be read to produce an open source health dashboard of all of our libraries.

This means that before working on this ticket, we need to create an action that achieves the above goal. Ideally, we could find one that does this already without having to create one, though it's doubtful that it would write information to artifacts (but perhaps it could write that information to a JSON file instead).

No files, tests, or entry points are identified in the issue. Start by determining how each package is installed and measured, then evaluate whether an existing GitHub Action can report size changes and preserve JSON or artifact data. Done means new pull requests receive byte and percentage changes for affected packages, with data retained for a future health dashboard.

Written by the indexing model from the issue text.