### 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.
Converted `custom-routes-proxying` example to TypeScript to match Contribution docs.
## Documentation / Examples
- [X] Make sure the linting passes by running `pnpm lint`
- [X] The examples guidelines are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing.md#adding-examples)