[Epic] Support declaring that a resource should be created only if it does not already exist

[justinvp]

There are some cases where there are cloud resources that are scoped to an account - like ServiceLinkedRoles in AWS or Project Services in GCP. Individual deployments will frequently want to ensure the resource exists - but do not want to manage it long term. For example:

1. If it exists, read it in so it can be referenced
2. If it does not exist, create it
3. When the Pulumi resource is deleted - don't remove from the cloud provider

Today, this can't quite be expressed in Pulumi. In principle it would be possible to provide a ResourceOption which would allow expressing this.

Related issues: #3388

Design

• Write design doc

Implementation Plan

TODO

Announce

• Documentation updates for this new capability
• Write blog post
• 🍦