Fix consolidated storage settings

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/52750 broke
consolidated storage settings because it was scanning storage-specific
settings. For example, let's say you had:

```yaml
object_store:
    enabled: true
    objects:
        artifacts:
            enabled: false

artifacts:
    enabled: true
```

In `1_settings.rb`, `ObjectStoreSettings#legacy_parse!` will
automatically add default `object_store` settings to the
storage-specific settings:

```yaml
artifacts:
    enabled: true
    object_store:
        enabled: false
        ...
```

As seen above, `artifacts.object_store.enabled` defaults to `false`, so
the check introduced in
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/52750 would mean
that object storage would never be enabled unless storage-specific
settings were also enabled.

The right fix: skip parsing of consolidated settings only if the object
type has explicitly disabled it in the consolidated settings. In the
example above, this means we check the parameter in
`object_store.objects.artifacts.enabled`, which overrides the default
consolidated settings.

This should fix https://gitlab.com/gitlab-org/gitlab/-/issues/233826.

config/object_store_settings.rb

@@ -124,9 +124,12 @@ class ObjectStoreSettings
       target_config = common_config.merge(overrides.slice(*ALLOWED_OBJECT_STORE_OVERRIDES))
       section = settings.try(store_type)
 
-      next unless uses_object_storage?(section)
+      # Admins can selectively disable object storage for a specific
+      # type as an override in the consolidated settings.
+      next unless overrides.fetch('enabled', true)
+      next unless section
 
-      if target_config['bucket'].blank?
+      if section['enabled'] && target_config['bucket'].blank?
         missing_bucket_for(store_type)
         next
       end
@@ -146,20 +149,6 @@ class ObjectStoreSettings
 
   private
 
-  # Admins can selectively disable object storage for a specific type. If
-  # this hasn't been set, we assume that the consolidated settings
-  # should be used.
-  def uses_object_storage?(section)
-    # Use to_h to avoid https://gitlab.com/gitlab-org/gitlab/-/issues/286873
-    section = section.to_h
-
-    enabled_globally = section.fetch('enabled', false)
-    object_store_settings = section.fetch('object_store', {})
-    os_enabled = object_store_settings.fetch('enabled', true)
-
-    enabled_globally && os_enabled
-  end
-
   # We only can use the common object storage settings if:
   # 1. The common settings are defined
   # 2. The legacy settings are not defined

spec/config/object_store_settings_spec.rb

@@ -130,13 +130,14 @@ RSpec.describe ObjectStoreSettings do
         end
       end
 
-      context 'when object storage is selectively disabled for artifacts' do
+      context 'when object storage is disabled for artifacts with no bucket' do
         before do
           config['artifacts'] = {
             'enabled' => true,
-            'object_store' => {
-              'enabled' => false
+            'object_store' => {}
           }
+          config['object_store']['objects']['artifacts'] = {
+            'enabled' => false
           }
         end