HDDS-14517. [Recon] Include all storage report fields in CSV report for Capacity Distribution

[priyeshkaratha]

What changes were proposed in this pull request?

This pull request simplifies how datanode storage metrics are downloaded. Instead of having multiple endpoints, the download logic is now handled by a single improved endpoint. The old endpoint that only supported pending deletion data has been removed. The new endpoint generates a detailed CSV with all relevant storage metrics, giving a more complete view of datanode health and usage.

• Refactored Datanode Metrics Download: The dedicated /download endpoint for pending deletion metrics in PendingDeletionEndpoint has been removed.
• Consolidated Storage Report: A new /download endpoint has been introduced in StorageDistributionEndpoint to provide a comprehensive CSV report.
• Expanded Report Fields: The new CSV report now includes all datanode storage fields such as Capacity, Used Space, Remaining Space, Committed Space, Reserved Space, Minimum Free Space, and Pending Block Size.
• Frontend URL Update: The frontend application (capacity.tsx) has been updated to use the new consolidated download URL.
• Updated Test Coverage: Corresponding unit tests have been removed from TestPendingDeletionEndpoint and new, comprehensive tests have been added in TestStorageDistributionEndpoint for the new download functionality.

What is the link to the Apache JIRA

HDDS-14517

How was this patch tested?

Tested using modified testcases.

[priyeshkaratha]

Hi @devabhishekpal @devmadhuu @ArafatKhan2198 can you please review the changes?