New Code Action: Add missing required attribute

[radeksimko]

Background

We currently report the following configuration as invalid:

output "foo" {

}

Users would also benefit from an easier way of addressing that diagnostic.

Proposal

• Provide code action which generates [snippet for] the missing attribute based on its constraint

Implementation Notes

It is not clear whether/how we could leverage snippet markers in the generated code (text edits) or whether this would have to be static text which cannot be tabbed through. Hence the needs-research label.