Introduces the storage-purchased data-testid

What does this MR do and why?

With the introduction of excess_storage_breakdown_card, we need to introduce data-testid="purchase-more-storage" similar to total_storage_available_breakdown_card.

Related to customers-gitlab-com#7516 (comment 1561748214)

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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.