Bind schemas to factory files, add support for groups in VPC-SC schema

[wiktorn]

Groups and principals are available in preview

Inspired by #2489, though this means that JSON schema is more strict than variables.tf

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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

[ludoo]

Ca we retrofit the validation to variables.tf in both vpc-sc module and FAST stage?

[ludoo]

yaml.schemas does not seem to work

[wiktorn]

yaml.schemas does not seem to work

Are you running multi-root workspace? Then this may be applicable, and you need specify yaml.schemas in root of the multi root workspace project.

[ludoo]

yaml.schemas does not seem to work

Are you running multi-root workspace? Then this may be applicable, and you need specify yaml.schemas in root of the multi root workspace project.

single root, but probably started as multiroot... :)