Add support to windows-startup-script-ps1 on Packer GCP (Terraform already supports this feature)

[hc-github-team-packer]

This issue was originally opened by @lmayorga1980 in https://github.com/hashicorp/packer/issues/10342 and has been migrated to this repository. The original issue description is below.

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Description

According to https://www.packer.io/docs/builders/googlecompute.html#windows, is only possible to use the windows-startup-script-cmd when using GCP as the builder. Would it be possible to use an existing powershell script?

Use Case(s)

Powershell script uses a combination of cmdlets and native windows executables.

Potential configuration

metadata": { "windows-startup-script-ps1":  "scripts/user_data.ps1" },