Make storage alert text more dynamic

What does this MR do?

• Pulls in namespace limit instead of always showing 10GB
• Pluralizes "You have reached the free storage limit of 10GB on 1 project."

No changelog since this sits behind the disabled additional_repo_storage_by_namespace feature flag

Screenshots

Before	After

Testing this locally

Requires EE edition

Paste the following into your Rails console

# Match the 10GB limit on GitLab.com, enable application setting
ApplicationSettings::UpdateService.new(Gitlab::CurrentSettings.current_application_settings, nil, { repository_size_limit: 10240, automatic_purchased_storage_allocation: true }).execute

ACCESS_LEVEL_OWNER = 50
PACKAGE_SIZE_IN_MIB = 10240

Feature.enable(:additional_repo_storage_by_namespace)
Feature.enable(:buy_storage_link)

def create_group_with_usage_and_additional_storage(owner, group_name, nr_of_packs_purchased, usage)
  group = Group.create(name: group_name, path: group_name, type: 'Group')
  GroupMember.add_user(group, owner, ACCESS_LEVEL_OWNER)
  project = ::Projects::CreateService.new(owner, { namespace_id: group.id, name: 'project-' + group_name, path: 'project-' + group_name }).execute

  group.additional_purchased_storage_size = nr_of_packs_purchased * PACKAGE_SIZE_IN_MIB
  group.save!

  project.statistics&.destroy!

  project_statistics = ProjectStatistics.new(
    project_id: project.id,
    namespace_id: group.id,
    commit_count: 12,
    repository_size: usage * 3 / 5,
    lfs_objects_size: usage * 2 / 5
  )

  project_statistics.save!
end

root_user = User.where(username: 'root').first

create_group_with_usage_and_additional_storage(root_user, 'over-free-limit', 0, 20.gigabytes)

Navigate to http://localhost:3000/groups/over-free-limit/-/issues to see alert

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #247846