Stop wrapping yamldecode with try()

[sruffilli]

Per #1794, updating all factories to avoid wrapping yamldecode in try, to have terraform explicitly fail in case of a malformed yaml file.

Since empty yaml files result in yamldecode to fail, this PR also updates all yaml files used in factories, adding the comment below to advice the user on how to create an empty document.

---
# Terraform will be unable to decode this file if it does not contain valid YAML
# You can retain `---` (start of the document) to indicate an empty document.

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