Merge pull request #293 from PrivateStorageio/235.backup-and-recovery

docs/requirements.txt

docs/source/backup.rst

docs/source/conf.py

docs/source/designs/backup-recovery.rst

docs/source/designs/costs.rst

docs/source/index.rst

requirements/test.in

setup.cfg

setup.py

src/_zkapauthorizer/backup-recovery.yaml

src/_zkapauthorizer/tests/test_client_resource.py