test: Split up x509 user certificates

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What does this MR do and why?

test: Split up x509 user certificates

Reorganizing the x509 helpers to separate files for each user. This improves maintainability and clarity in the test suite.

Changelog: other

🛠️ with ❤️ at Siemens

References

Screenshots or screen recordings

How to set up and validate locally

1. Run the tests using X509Helpers::User1

   bundle exec rspec spec/lib/gitlab/git/tag_spec.rb spec/lib/gitlab/x509/commit_spec.rb spec/lib/gitlab/x509/signature_spec.rb spec/lib/gitlab/x509/tag_spec.rb spec/models/commit_signatures/x509_commit_signature_spec.rb spec/requests/api/graphql/project/tree/tree_spec.rb spec/tasks/gitlab/x509/update_rake_spec.rb

2. Run the tests using X509Helpers::User2

   bundle exec rspec spec/lib/gitlab/x509/commit_sigstore_spec.rb spec/lib/gitlab/x509/signature_sigstore_spec.rb spec/lib/gitlab/x509/tag_sigstore_spec.rb

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 style guides
• Conforms to the javascript style guides
• Conforms to the database guides
• Conforms to the merge request performance guidelines