services: admin: Export rottlog-configuration accessors.
* gnu/services/admin.scm (<rottlog-configuration>): Rename accessors
rottlog-rottlog to rottlog-configuration-rottlog, rottlog-rc-file to
rottlog-configuration-rc-file, rottlog-rotations to
rottlog-configuration-rotations, rottlog-jobs to rottlog-configuration-jobs.
(rottlog-etc, rottlog-jobs-or-default, rottlog-service-type): Adjust
accordingly.