Debian Package Manager MVC Technical debt

Summary

This issue is used to keep track of technical debt around Debian Package Manager.

See #5835 (comment 414103286).

Pure code refactoring / no user-visible changes

• Don't use symbols as keys in metadata (see !55896 (comment 532350725)) !57420 (merged)
• Unneeded index on packages_debian_{project,group}_architectures.distribution_id (See !51732 (comment 491491814)) !59615 (merged)
• define_distribution_for(:project) !53818 (comment 571112856)
• Refactor private/public distribution (see !62017 (comment 589658867))
• In lib/api/concerns/packages/debian_package_endpoints.rb we have authenticate_with and route_setting :authentication, authenticate_non_public: true. route_setting :authentication, authenticate_non_public: true should not be necessary. We should solely use authenticate_with.
• remove unused distribution attributes #335994 (closed) !66470 (merged)
• test rescue_from ActiveRecord::RecordInvalid !64923 (comment 636133188)

Other improvement:

• GDK support on MacOS (see !57413 (comment 543670230)) gitlab-development-kit!1925 (merged)
• Debian component files for usage statistics !53818 (comment 566963777)
• 🔥 Prune dangling incoming files (#367538 (closed) see !62028 (comment 584209391))
• Track distribution event (#350483 (closed) see !62017 (comment 589658893))
• remove distribution.needs_update? !71502 (merged)
• 🐛 re-generate distribution before expiration !64872 (closed) 👈
• Bring group distributions on par with project distributions:
  • Debian CRUD group distribution endpoints !66188 (merged)
  • 🐛 Ensure group distributions are generated on package upload #396960
• Remove Release and Release.gpg endpoints !64926 (comment 612943341) !65189 (closed) (abandoned)
• Doc uses PRIVATE-TOKEN header, while it's not accepted !71911 (merged)
• 🐛 When a package is uploaded and it references a codename not present in the project distributions, the second job is still enqueued (in #340307 (closed))
• Check debian distribution nested query performance #329928