[terraform/gcp] Split up regular and headless workspaces into separate nodepools

[adrienthebo]

Description

Related Issue(s)

See https://github.com/gitpod-io/gitpod/issues/12740

How to test

Create a preview environment with werft:

werft run github -j .werft/gke-installer-tests.yaml -a skipTests=true -a deps=external -a preview=true

Once the preview is up, login to the node and confirm that image builds run on headless workspace nodes and workspaces run on regular-workspace nodes.

Release Notes

[terraform/gcp] Run regular and headless workspaces on separate node pools

Documentation

Werft options:

• [ ] /werft with-preview
• [ ] /werft with-integration-tests=all Valid options are all, workspace, webapp, ide