Protected packages: Return ServiceResponse in Pypi CreatePackageService

What does this MR do and why?

• Returning a successful ServiceResponse as suggested by the best-practice documentation, see https://docs.gitlab.com/ee/development/reusing_abstractions.html#serviceresponse
• Exceptions raised in Packages::Pypi::CreatePackageService have been transformed to erroneous service response
• This MR follows the same approach as in another MR related to npm packages

🛠 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 Protected packages: Align return object of npm ... (!140010 - closed)

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/pypi_packages_spec.rb spec/services/packages/pypi/create_package_service_spec.rb

Related to #427546