fix(kas): document rewrap proto fields used in bulk flow (#2826)

### Proposed Changes

* Adds descriptions to the rewrap request and response proto fields for
clarity

### Checklist

- [ ] I have added or updated unit tests
- [ ] I have added or updated integration tests (if appropriate)
- [ ] I have added or updated documentation

### Testing Instructions

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Co-authored-by: Elizabeth Healy <ehealy@virtru.com>

Author: jakedoublev