Merge pull request #255 from PrivateStorageio/169.lease-maint-from-config

docs/source/configuration.rst

src/_zkapauthorizer/_plugin.py

src/_zkapauthorizer/config.py

src/_zkapauthorizer/lease_maintenance.py

src/_zkapauthorizer/tests/strategies.py

src/_zkapauthorizer/tests/test_lease_maintenance.py

src/_zkapauthorizer/tests/test_plugin.py