chore(v2): add build size bot workflow Github CI workflow

[jcs98]

Motivation

Feature for #3521

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

A comment is added to the PR with changes in the size of key built files

[netlify]

Deploy preview for docusaurus-2 ready!

Built without sensitive environment variables with commit 3d32594

https://deploy-preview-3744--docusaurus-2.netlify.app

[jcs98]

@slorber
This uses a repo token in the workflow to make a comment:
repo-token: '${{ secrets.GITHUB_TOKEN }}'
Can you please set it up?

[slorber]

Thanks @jcs98 , I'll see if I can get the token configured, as I don't have permission to add this secret myself

[slorber]

Not sure but maybe it will work automatically after I merge?
https://docs.github.com/en/free-pro-team@latest/actions/reference/authentication-in-a-workflow

let's see