HDDS-13197. Design doc for storage capacity distribution.

[priyeshkaratha]

What changes were proposed in this pull request?

This PR adds a detailed design proposal for Storage Capacity Distribution Dashboard in Apache Ozone. It includes the problem statement, goals, proposed CLI and Recon-based approaches, technical challenges, and output format for better observability into Ozone-used storage and deletion diagnostics.

The primary focus is on the Recon-based approach, and the CLI approach is included for reference but not being pursued due to complexity in large-scale clusters.

What is the link to the Apache JIRA

HDDS-13197

How was this patch tested?

NA