Add a usage quotas UI state for SaaS project limits = 0 state

What does this MR do and why?

Adds a new statistics card for Usage Quotas Storage tab, for cases when project limits are applied but no actual limits are enforced (project limits == 0).

Related to #429072

Screenshots or screen recordings

Before	After

How to set up and validate locally

You'll need a SaaS instance, with project limits set to 0. To set the project limits to 0, run in rails c:

Gitlab::CurrentSettings.update!(repository_size_limit: 0)

Alternatively, you can test this using storybook (http://localhost:9002/?path=/story/ee-usage-quotas-storage-namespace-storage-app--saas-with-no-limits).

MR acceptance checklist

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