docs: Terraform import COS

[MichaelThamm]

Issue

We want to be able to import a regular Juju deployment into Terraform state so that a user can either migrate to our products, or continue to manage their deployment with state.

Solution

Offer the convenient atelier import juju command.

Checklist

• I have added or updated relevant documentation.
• PR title makes an appropriate release note and follows conventional commits syntax.
• Merge target is the correct branch, and relevant tandem backport PRs opened.
• This PR has Terraform product changes and appropriate lifecycle args and moved blocks were added to the terraform/*/upgrades.tf file(s).
• This PR has breaking changes to the product API(s) and I have created an issue in SolQA pipelines to address this.

Context

Testing Instructions

I tested both import workflows in the doc manually:

1. Deploy COS Lite (track/2)
2. Removed the state files
3. Import
4. terraform plan

Upgrade Notes