Monitor bundle size changes for PRs

[tomalec]

Given we are in a more relaxed time, maybe we would like to improve also our automation and GH tooling?

In the past we were facing some constraints for plugin.zip size, still, we would like to deliver less than more JS to the end customer. Maybe we could use some automation, to monitor if something goes off or provides a traffic benefit for the end-users.

Currently, our main js bundle has 718KB gzipped, which is pretty big IMHO.

User story

As a developer publishing PR or reviewing one, I'd like to easily monitor how the change affects the final bundle size.

Technical

We could use something like
https://github.com/siddharthkp/bundlesize

or https://github.com/bundlewatch/bundlewatch

I guess it should work as well for js as any other file.

Additional comments

@jconroy are we fine with authorizing the app?