feat: show the resources to the user that would be deleted

[asalkeld]

When running "nitric down", first run the pulumi preview to gather the resources that would be deleted then present these to the user to confirm.

from: https://github.com/nitrictech/cli/pull/160#discussion_r822119040

If possible, a better approach might be to show the things being destroyed

"Warning - the following resources will be destroyed:" Type Name Plan

Stack quickstart-dev delete
├─ aws:s3:BucketObject index.html delete
└─ aws:s3:Bucket my-bucket delete

Also see: https://www.pulumi.com/docs/get-started/aws/destroy-stack/