chore: release 9.0.0

[release-please]

🤖 I have created a release *beep* *boop*

9.0.0 (2020-05-07)

⚠ BREAKING CHANGES

• Beta clusters have changed the default to use the GKE_METADATA_SERVER, to use the old option set node_metadata = "SECURE".
• Minimum provider change increased to 3.19.
• The ACM module has been refactored and resources will be recreated. This will show up in Terraform plans but is a safe no-op for Kubernetes.
• Minimum Google provider version increased to 3.16.
• For the safer cluster module, you must now specify release_channel instead of kubernetes_version.

Features

• [safer-cluster] Replace "kubernetes_version" with "release_channel" (#487) (5791ac1)
• Add an auth submodule outputting a kubeconfig (#469) (a5ace36)
• Add config sync module (#493) (c090d5b)
• Add fully configurable resource usage export block in GA and upgrade GCP provider (#491) (54eca6b)
• Add GCE PD CSI Driver beta support (#497) (d96afa7)
• Add support for setting firewall rules (#470) (16bdd6e)
• Enable GKE_METADATA_SERVER as default node_metadata for beta-clusters (#490) (#512) (8e14762)
• Expose the grant_registry_access variable in safer-cluster (#509) (0961613)

Bug Fixes

• Correct identity namespace output for beta clusters (#500) (c783659), closes #489

---

This PR was generated with Release Please.

[morgante]

Waiting for:

• Feature/config sync module #493
• Upgrade guide