fix(cli): deploy and destroy with --all option fails on apps with no top-level stacks

[go-to-k]

NOTE: I will close this if it meets the specifications. Waiting for review in the PR, so I will decide it based on the response.

TODO: Consider what to do when there are stages and stacks at the top level.

When running cdk destroy --all or cdk deploy --all against a configuration with no top-level stacks (nested stages only), the following error occurs. This PR fixes the behavior.

const app = new cdk.App();

new MyStage(app, 'MyStage'); // This has CdkSampleStack

> cdk deploy
Since this app includes more than a single stack, specify which stacks to use (wildcards are supported) or specify `--all`
Stacks: MyStage/CdkSampleStack

> cdk deploy --all
...
No stack found in the main cloud assembly. Use "list" to print manifest

> cdk destroy --all
...
No stack found in the main cloud assembly. Use "list" to print manifest

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.64%. Comparing base (2a6f8d3) to head (9550003).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #985      +/-   ##
==========================================
+ Coverage   87.38%   87.64%   +0.26%     
==========================================
  Files          71       72       +1     
  Lines       10010    10030      +20     
  Branches     1311     1322      +11     
==========================================
+ Hits         8747     8791      +44     
+ Misses       1240     1215      -25     
- Partials       23       24       +1     

Flag	Coverage Δ
suite.unit	87.64% <100.00%> (+0.26%)	⬆️

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