PB-6908: Fix Default VSC CSISnapshotName to CSISnapshotMap Conversion

[pallav-px]

What type of PR is this?

Uncomment only one and also add the corresponding label in the PR: bug feature improvement cleanup api-change design documentation failing-test unit-test integration-test

What this PR does / why we need it: We need to Migrate the CSISnapshotName to CSISnapshotMap in case "default" is given to convert and find the default VSC for all provisioner in case user has not updated the PX Backup to 2.7.0

Does this PR change a user-facing CRD or CLI?:

no

Is a release note needed?:

yes

Issue:
User Impact:
Resolution

Does this change need to be cherry-picked to a release branch?:

yes 24.3.X