Storage Capacity Tracking Changes for csi-powerflex

[VamsiSiddu-7]

Description

This pr adds the changes in the GetCapacity Rpc call to support the Storage Capacity tracking for csi-powerflex

GitHub Issues

List the GitHub issues impacted by this PR:

GitHub Issue #
dell/csm#876

Checklist:

• I have performed a self-review of my own code to ensure there are no formatting, vetting, linting, or security issues
• I have verified that new and existing unit tests pass locally with my changes
• I have not allowed coverage numbers to degenerate
• I have maintained at least 90% code coverage
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• Backward compatibility is not broken

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Please also list any relevant details for your test configuration

• I have tested the following scenarios
  1. Installed the csi-powerflex driver enabling the storage capacity in the values.yaml.
  observations:
  the driver installation is successful
  the storage capacity objects are created with the available capacity
  2. Run volume helm test for both thick and thin provisioning
  I am able to verify the GetCapacity call is showing correct available capacity