Google Cloud - Support for CMEK for VM disk which are created for image creation

_This issue was originally opened by @kamaltherocky in https://github.com/hashicorp/packer/issues/11272 and has been migrated to this repository. The original issue description is below._

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#### Description
Currently, Packer only supports creating the new image using CMEK but for disks which are created in the VM used for creating the image.

We have enforced CMEK key for all disks in GCP, so when we run the packer to create an image, the VM is created with a Disk that is not encrypted with CMEK, so security control detects and deletes those VM and disk.

It would be good if the VM created by Packer can build the VM disk with the CMEK key passed to the builder.

#### Use Case(s)

Any relevant use-cases that you see.

#### Potential configuration

```
disk_encryption_key = "CMEK Key Resource ID"
```

#### Potential References
Current support for CMEK for images - https://www.packer.io/docs/builders/googlecompute#image_encryption_key