New NEXTCLOUD_EXEC_USER environment variable added which allows control over which
user is used to execute cron tasks inside the Nextcloud container. By default, the
user is `www-data`. If the environment variable is specified but empty, no `--user`
option is provided to `docker exec`.
Mount individual shell scripts (with the `*.sh` extension) inside `/cron-scripts/` in the
container. The cron daemon will automatically run these scripts inside the Nextcloud
container for you. Write the scripts as if they will run in the Nextcloud container
itself.
