`${config-lines:<key>:<prefix>[:mib-bytes]}` in a file's content writes one line
per entry (nothing for an unset value or empty list; a newline in an entry
refuses the composition); `${config-json}` writes the module's set config values
as one JSON object. Both join the sweep's table of fillers. Their rows join the
config table test (A-22).
Builds: design 42 zfs-owns-zfs §3, §9; answers A-15, A-24, A-22