WIP: Make structured APT mandatory

[quba42]

What are the changes introduced in this pull request?

Right now, "structured APT" for deb type content is an optional feature that can be enabled or disabled using a setting.

With this PR all users upgrading to a Katello version with these changes will be migrated to use structured APT. The code is cleaned up to reflect the assumption that all deb type content will use structured APT hence forth.

Considerations taken when implementing this change?

Everything is based on the assumption that lib/katello/tasks/upgrades/4.19/enable_structured_apt_for_deb.rake will be run during upgrade to Katello 4.19. This is essential because the new code assumes there is no deb content left that was not migrated by the rake task. Is this a safe assumption?

What are the testing steps for this pull request?

1. Create some deb type content on your instance without these changes (make sure structured APT is disabled for this).
2. Apply these changes.
3. Run the rake task (should happen automatically when using a proper upgrade path).
4. Re-sync any deb content to any smart proxies.
5. Check that all deb content still works and is using structured APT mode.

Summary by Sourcery

Make structured APT mandatory for all deb repositories by removing the feature toggle, cleaning up related code paths, consolidating Pulp API interactions, and providing a migration task to convert existing repos to the new mode.

New Features:

• Add a Rake upgrade task to migrate existing Debian repos to structured APT mode.

Enhancements:

• Remove the optional structured APT feature flag and assume all deb content uses structured APT.
• Consolidate Pulp API access with new pulp_primary_api, pulp_components, and pulp_distributions methods.
• Simplify and clean up legacy logic by removing conditional checks and helper methods for non-structured APT workflows.
• Remove the deb_enable_structured_apt plugin setting and related configuration toggles.

Tests:

• Update test expectations to reflect the always-on structured APT behavior.

[sourcery-ai]

Reviewer's Guide

This PR removes the optional structured APT setting, making all deb content use structured APT by default. It centralizes Pulp API interactions in the Apt service, refactors repository URL handling, updates action and controller code to treat deb repos uniformly, and delivers a one-off rake task to migrate existing repos during upgrade.

File-Level Changes

Change	Details	Files
Centralize Pulp API calls and structured APT logic in the Apt service	Introduce pulp_primary_api to always target the main Pulp server Implement pulp_components and pulp_distributions with content_release_components_api Add sanitize_pulp_distribution helper Simplify mirror_remote_options to use pulp_distributions Refactor version_missing_structure_content? and publication_options to use the centralized API	app/services/katello/pulp3/repository/apt.rb
Eliminate optional structured APT toggles and settings	Remove deb_using_structured_apt? delegate and root_repository method Drop 'deb_enable_structured_apt' plugin setting Clean up legacy structured/simple branching in models	app/models/katello/root_repository.rb lib/katello/plugin.rb
Refactor repository content URL and metadata handling	Update deb_content_url_options to use backend_service.pulp_components/distributions Remove legacy deb_pulp_components, deb_pulp_distributions, and sanitize methods Ensure content URL is always built for deb repos	app/models/katello/repository.rb
Uniformly apply deb_content_url_options in actions and controllers	Replace conditional deb_using_structured_apt? checks with deb? guards Always append deb_content_url_options in content_create, content_update, sync, and finish_upload actions Remove structured-atp branches in destroy, clone_contents, and API controller	app/lib/actions/katello/repository/sync.rb app/lib/actions/candlepin/product/content_create.rb app/lib/actions/candlepin/product/content_update.rb app/lib/actions/katello/repository/destroy.rb app/lib/actions/katello/repository/clone_contents.rb app/lib/actions/katello/repository/create.rb app/lib/actions/katello/repository/finish_upload.rb app/lib/actions/katello/product/content_create.rb app/lib/actions/katello/product/content_destroy.rb app/lib/actions/katello/content_view/refresh_rolling_repo.rb app/controllers/katello/api/v2/repositories_controller.rb
Add upgrade task to migrate existing APT repos to structured mode	Introduce lib/katello/tasks/upgrades/4.19/enable_structured_apt_for_deb.rake Remove old migrate_structure_content_for_deb.rake	lib/katello/tasks/upgrades/4.19/enable_structured_apt_for_deb.rake
Update tests to match mandatory structured APT behavior	Remove expectations of deb_using_structured_apt? in tests Assert nil structured/simple flags in publication options Rename and adjust test cases to reflect deb? usage	test/services/katello/pulp3/repository/apt/apt_test.rb test/actions/katello/repository_test.rb test/controllers/api/v2/host_subscriptions_controller_test.rb test/models/product_content_test.rb

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[maximiliankolb]

FYI: I created a docs PR that is blocked until this is merged: theforeman/foreman-documentation#4215