feat: restructure how var files are provided to workflow templates

[Liam-Johnston]

---

Checklist

I applicable, I acknowledge that I have:

• Read the contributing guide
• Ran terraform fmt on all modified files
• Regenerated the relevant README.md files using tools/tfdoc.py
• Made sure all relevant tests pass

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[ludoo]

Can you please

• explain the use-case and rationale of your change
• target fast-dev as we do FAST development there

[Liam-Johnston]

Hey @ludoo,

The reason this is being implemented is because the stage 2-project-factory references variables from the stage 2-networking which currently don't get included in the github or gitlab workflow file that is generated by the 1-resource-management stage. see HERE

This change modifies the way the template file variables are populated in the 1-resource-management stage to follow a similar pattern to the way it works in the 0-bootstrap stage.