* New DEBUG environment variable enables `set -x` in shell scripts for
extra verbose output for debugging custom cron scripts and to assist
with development of the core scripts.
* Verify if we can find the Nextcloud container on start up. Fail if
not.
* Print information about how we will search for Nextcloud on start up.
* During cron task execution, the ID of the Nextcloud container is
printed, if found.
If the Nextcloud container is recreated while the cronjob container is still running, the ID of the
container is obtained each time the cron tasks are executed. Previously it was cached on entrypoint,
so if the ID changed this container would fail.
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.
