Protected packages: Return ServiceResponse for CreateNpmPackageService

What does this MR do and why?

Protected packages: Return ServiceResponse for CreateNpmPackageService

MR includes:

• Returning a successful ServiceResponse as suggested by the best-practice documentation, see https://docs.gitlab.com/ee/development/reusing_abstractions.html#serviceresponse

• This MR depends on Protected packages: Align return object of npm ... (!140010 - closed)

🛠️ with ❤️ at Siemens

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

MR Checklist (@gerardo-navarro)

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the javascript style guides
• Conforms to the database guides
• Wait for !140010

Screenshots or screen recordings

Only backend changes. No frontend changes.

How to set up and validate locally

1. Execute the relevant tests

bundle exec rspec ./spec/requests/api/npm_project_packages_spec.rb spec/services/packages/npm/create_package_service_spec.rb

Related to #323970 (closed)