feat: support GCE machine configs

[matttrach]

tracking #1517

[matttrach]

https://github.com/rancher/terraform-provider-rancher2/releases/tag/v8.0.0-rc4
https://github.com/rancher/terraform-provider-rancher2/releases/tag/v7.3.0-rc3
https://github.com/rancher/terraform-provider-rancher2/releases/tag/v6.7.0-rc1

[Josh-Diamond]

All sub-issues have been validated + closed