We use `timeout` from the coreutils package (should be part of many basic
installations - maybe with a different name) to force the individual
healthcheck commands too exit after a predefined timeout (300s); if this
doesn't help, send a SIGKILL.

This should help with the initial problem of hanging. A next step should
be to catch the `timeout` invoked exit and log this as an exceptional
happening.

Address #60

Instead of an external CronJob pod, or a supervisord cron daemon, we use
a subshell. Also we assume, the regular cronjob *also* needs to run when
the container starts. Insofar, we start the subshell, make sure it runs
a single time (and continues in the background) and then continue with
starting clarin-dspace.

Address #48

Sync config with https://gitlab.inf.unibz.it/commul/docker/commons/blob/master/helm-charts/webserver/nginx.conf

This reverts commit 9717f5b1 because
withwith #35 fixed 'xmlui.session.ipcheck' can be safely used again.

Prefix (oai/requeststripped) and add entries in robots.txt.

- sitemaps are now generated in the entrypoint script