feature: add -n shortcut for --namespace flag in generate command

[YhebBOUSSELMI]

Description

Fix #275
Add -n shortcut for the --namespace flag.

What does this PR do?

Adds a -n shortcut for the --namespace flag, consistent with how other shortcuts are implemented in the project.

    # ./score-k8s generate --help
    -n, --namespace string                An optional namespace to set for all generated resources

     # Before
     ./score-k8s generate score.yaml --namespace=test-ns

    # After (shortcut added)
    ./score-k8s generate score.yaml -n test-ns 

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• New chore (expected functionality to be implemented)

Checklist:

• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• I've signed off with an email address that matches the commit author.

[mathieu-benoit]

Thanks for your contribution, @YhebBOUSSELMI.

Even if it was a good idea, I requested some changes to keep these other messages simple and consistent with other parameters (and I think that's what other CLIs do too).

Also, can you fix the unit tests by running them locally make test too please?

[mathieu-benoit]

You just need to fix the DCO here https://github.com/score-spec/score-k8s/pull/277/checks?check_run_id=69945366786, typically running this locally:

git rebase HEAD~2 --signoff
git push --force-with-lease origin feature/add-shortcut-param-for-generate-namespace

Other than that, this LGTM!

[mathieu-benoit]

LGTM