Add security nav tabs in a dedicated method

What does this MR do?

In order to reduce cyclomatic and perceived complexity in the EE::ProjectsHelper#get_project_nav_tabs method, some of its code has been moved to a dedicated method.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• [-] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

I did not add tests because the new method is implicitly tested by get_project_nav_tabs' specs, which feels sufficient to me.

• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Closes #219268 (closed)