Change container_registry_enabled readers to check user permissions

What does this MR do?

We are in the process of migrating code to use ProjectFeature#container_registry_access_level instead of Project#container_registry_enabled.

With projects.container_registry_enabled, the container registry had the same visibility as the project. So if the project is public, the container registry is public. Now, with projects.container_registry_access_level, if container_registry_access_level is set to PRIVATE, the container registry should be private even if the project is public.

project_features.container_registry_access_level can currently contain the following values, ENABLED and DISABLED. This mimics the behavior of projects.container_registry_enabled. Before we start allowing the 3rd possible value (PRIVATE), we need to ensure that all locations where we check if the container registry is enabled should be changed to check if the container registry is enabled for the current user/actor.

This MR updates 2 such locations:

1. app/finders/container_repositories_finder.rb
2. app/helpers/packages_helper.rb

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Does this MR meet the acceptance criteria?

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• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
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• This change is backwards compatible across updates, or this does not apply.

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• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
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Security

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Related to #18792 (closed)