fix panic when inferring stack with empty image

[andreafalzetti]

Proposed changes

Fixes DEV-368

This PR fixes a panic that is caused when using Docker Compose and Okteto Manifests together and the Image field of the service is empty. For example, when running okteto down or okteto destroy the image is not built, which may cause the image field to be empty, in case the compose rely on built-in Okteto Variables such as ${OKTETO_BUILD_<SERVICE>_IMAGE}

This is a panic that was introduced in 2.27.x because of recent changes.

How to validate

1. Using https://github.com/okteto/movies-with-compose
2. Change services.app.image to ${OKTETO_BUILD_APP_IMAGE}
3. Create the following okteto.yml

build:
  app:
    context: api
deploy:
  compose: docker-compose.yml

4. Run okteto build and observe the panic
5. Now repeat with the new build and validate that the panic does not occurr
6. Now test that deploy + up + down and destroy work as expected and cause no panics.

CLI Quality Reminders 🔧

For both authors and reviewers:

• Scrutinize for potential regressions
• Ensure key automated tests are in place
• Build the CLI and test using the validation steps
• Assess Developer Experience impact (log messages, performances, etc)
• If too broad, consider breaking into smaller PRs
• Adhere to our code style and code review guidelines

[andreafalzetti]

goland insists in removing this, which is redundant, happy to revert it if we prefer so.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 43.09%. Comparing base (19eb936) to head (488a3c3).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4312      +/-   ##
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- Coverage   43.10%   43.09%   -0.01%     
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  Files         371      371              
  Lines       30021    30025       +4     
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  Hits        12940    12940              
- Misses      15954    15956       +2     
- Partials     1127     1129       +2