feat: add stack output values

[AntoineMontane]

Related issue

Fixes #264

Description

Add stack output values to the action output

Checklist

• I have updated the PR title to match CDKTF's style guide
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works if applicable
• New and existing unit tests pass locally with my changes

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