Bump Terraform provider and update config accordingly

[henrybell]

Background

This bumps the Google Terraform provider to the most recent 5.xx version (as a result of a recent breaking change), and additionally includes associated updates to the Terraform config:

• Bring the config into line with the new provider as it relates to Config Sync (i.e. include enabled = true)
• Remove direct use of the google-beta provider (though it is still used by some dependencies)
• Switch off the now-default deletion protection for the GKE clusters (for ease of testing)

Additional Notes

This PR is marked as draft until further updates are available on the Config Sync breaking change.