### Reason for making this change
https://yarnpkg.com/getting-started/qa#:~:text=yarn%2Finstall%2Dstate.,your%20workspaces%20all%20over%20again.
In the official documentation of `yarn`, it is stated that `.yarn/install-state.gz` is an optimization file that developer shouldn't ever have to commit. However, currently, when running `create-next-app`, `.yarn/install-state.gz` is being commited.
### Remaining work
I apologize for only modifying one template initially to initiate the discussion first.
If this change is agreed upon, it should be synchronized with other `.gitignore` templates. Would it be possible to follow a similar approach as in https://github.com/vercel/next.js/pull/47241? I would appreciate any assistance in syncing this change.
* Only copy .gitignores to examples that are actual packages.
`custom-server` is just a `.md` redirecting users to the documentation.
* Add .gitignores to examples that lack them