Investigate simplifying HardDeletes for encrypted Blobs

With encryption at rest being worked on for new uploads, may be we can simplify HardDeletes for those encrypted blobs by simply hard deleting the encryption key and w/o touching the entire blob content. This will greatly reduce the I/O burden on the disk as we need to touch only the key which is way smaller in size compared to blob content.

Start by tracing the HardDeletes path for encrypted blobs and identifying how encryption keys and blob content are currently handled. Determine whether removing only the encryption key preserves hard-delete behavior and document the required design, affected components, and validation needed.

Written by the indexing model from the issue text.