Similar to #26993.

What problem does this address?

It takes ages to finish:

git clone git@github.com:WordPress/gutenberg.git

At the moment the size of the repository is over 2GB!!!!

If you add to the mix that you need to run on every brand new repository:

npm install

It adds another 1GB of data that needs to be downloaded as reported in #26993.

What is your proposed solution?

It makes me think that maybe gh-pages branch is one of the reasons why the size of the repository has grown so much. We replace the content of gh-pages with the new build of Storybook on every commit to the main branch.

I don't know how this sort of issues are usually solved in git-based repositories, but the comment from WordPress Slack (link requires registration at https://make.wordpress.org/chat/) authored by @ocean90 should be a good start:

https://wordpress.slack.com/archives/C5UNMSU4R/p1609864617204200?thread_ts=1609770083.149700&cid=C5UNMSU4R

Yes by creating a new orphan branch from gh-pages. You have to add the files there and the gh-pages branch needs to be deleted. Then rename the new branch to gh-pages which finally gets force-pushed.
This post documents the steps

The link included:
https://medium.com/@sangeethkumar.tvm.kpm/cleaning-up-a-git-repo-for-reducing-the-repository-size-d11fa496ba48

This article contains some techniques that could help with gh-pages where we don't care about history at all. There are also several interesting references to other similar articles that try to address similar issues.