Add bundlesize config

[jahvi]

Related issues

#1293, #1294, #1966

Short description and why it's useful

There's been a few issues targeted at improving the bundle size, integrating bundlesize in the CI checks should help keep track of how the bundles are changing across commits and PRs so it's easier to see how big or small they get. You can check this dummy PR in my fork that adds an extra library that makes the bundle size bigger than the set maximum.

I'm just adding the app, vendor and manifest files to the check with some sensible maximum file sizes but this can be tweaked.

Screenshots of visual changes before/after (if there are any)

PR Screen

Bundle Size Details

Screenshot of passed e2e tests (if you are using our standard setup as a backend)

TBA

Upgrade Notes and Changelog

• No upgrade steps required (100% backward compatibility)
• I've updated the Upgrade notes and Changelog on how to port existing VS sites with this new feature

Contribution and currently important rules acceptance

• I read and followed contribution rules
• I read the TypeScript Action Plan and adjusted my PR according to it
• I read about Vue Storefront Modules and I am aware that every new feature should be a module

[filrak]

Great addition, thank you! ;)

[jahvi]

Thanks! Keep in mind that to make the check show in PRs someone with admin rights needs to authorise bundlesize with travis as shown in their readme:
https://github.com/siddharthkp/bundlesize#2-build-status