Helm chart download API endpoint [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

Helm charts package registry API download endpoint. i.e:

GET /api/v4/projects/<id>/packages/helm/<channel>/charts/<name>-<version>.tgz

This is item 3.2 of #18997 (comment 530270349)

Explain plan

The code has:

          package_file = Packages::PackageFile.for_helm_with_channel(authorized_user_project, params[:channel])
                                              .preload_helm_file_metadata
                                              .with_file_name("#{params[:file_name]}.tgz")
                                              .last!

The corresponding query:

(byebug) print Packages::PackageFile.for_helm_with_channel(authorized_user_project, params[:channel])
                                              .preload_helm_file_metadata
                                              .with_file_name("#{params[:file_name]}.tgz")
                                              .reverse_order!.limit(1).to_sql

SELECT
    "packages_package_files".*
FROM
    "packages_package_files"
    INNER JOIN "packages_packages" ON "packages_packages"."id" = "packages_package_files"."package_id"
    INNER JOIN "packages_helm_file_metadata" ON "packages_helm_file_metadata"."package_file_id" = "packages_package_files"."id"
WHERE
    "packages_packages"."project_id" = 1
    AND "packages_packages"."package_type" = 11
    AND "packages_packages"."status" = 0
    AND "packages_helm_file_metadata"."channel" = 'stable'
    AND "packages_package_files"."file_name" = 'package-1-v1.0.1.tgz'
ORDER BY
    "packages_package_files"."id" DESC
LIMIT 1;

https://explain.depesz.com/s/ykBS

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