Limit storage banners to namespaces with project storage enforced

What does this MR do and why?

It limit the storage notifications to namespaces with project-level storage enforcement enabled.

Screenshots or screen recordings

project-level storage enforcement	namespace-level storage enforcement

How to set up and validate locally

The namespace storage page have different views (that's being consolidated into one with #375651), to make sure you're always on the correct "cards" view apply this patch (e.g. copy the whole code then in terminal run pbpaste | git apply -):

diff --git a/ee/app/assets/javascripts/usage_quotas/storage/components/namespace_storage_app.vue b/ee/app/assets/javascripts/usage_quotas/storage/components/namespace_storage_app.vue
index 4df6d0636ab0..1846f39e6d54 100644
--- a/ee/app/assets/javascripts/usage_quotas/storage/components/namespace_storage_app.vue
+++ b/ee/app/assets/javascripts/usage_quotas/storage/components/namespace_storage_app.vue
@@ -216,7 +216,7 @@ export default {
       :additional-purchased-storage-size="namespace.additionalPurchasedStorageSize"
       :actual-repository-size-limit="namespace.actualRepositorySizeLimit"
     />
-    <div v-if="isAdditionalStorageFlagEnabled && storageStatistics">
+    <div v-if="storageStatistics">
       <storage-usage-statistics
         v-if="shouldUseNewStorageDesign"
         :storage-limit-enforced="storageLimitEnforced"

1. Navigate to a namespace that has a project (where you're the owner of)
2. From left sidebar go to: Settings > Usage Quotas > Storage tab

To have project-level storage enforcement enabled

1. Disable namespace_storage_limit feature flag, in rails console run: Feature.disable(:namespace_storage_limit)
2. Make sure ::Gitlab::CurrentSettings.automatic_purchased_storage_allocation? is false (in console run: ::Gitlab::CurrentSettings.update(automatic_purchased_storage_allocation: false))
3. Ensure the notification is showing (above the cards)

To have namespace-level storage enforcement enabled

1. Enable namespace_storage_limit feature flag, in rails console run: Feature.enable(:namespace_storage_limit)
2. Make sure ::Gitlab::CurrentSettings.automatic_purchased_storage_allocation? is true (in console run: ::Gitlab::CurrentSettings.update(automatic_purchased_storage_allocation: true))
3. Ensure the notification is not showing

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #371963