Make aws_iam_policy_attachment warning less opaque

[mcwqy9]

The current note on aws_iam_policy_attachment is well intentioned but too subtle. I managed to revoke an execution role from 7 lambdas over this. I'm not alone. Consider #94, and #133, which feature gems like:

"aws_iam_policy_attachment as it is implemented today is insanely dangerous" and
"this is hugely disruptive and downright dangerous to use in a live environment. Folks should probably stick with using aws_iam_role_policy_attachment instead of aws_iam_policy_attachment"

I actually think aws_iam_policy_attachment ought to be removed from Terraform because no one expects the Terraform inquisition, but at the very least we can make the docs clearer.

This update is worth deploying to the site immediately.

[grubernaut]

LGTM, thanks!

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!