Remove google-beta provider, as resources are now available on stable.

I just used this repo as a template for bootstraping my own configuration (it is great, by the way, thanks !), and could do so without using the google-beta provider.

I deduct that the version of the google provider that I used (4.36.0) considers those resources stable.

I therefore suggest that we update the example to reflect that fact.

You might want to update the .terraform.lock.hcl, or maybe add an explicit minimum version in your config along this change.