Use systemd-startscript

[neufeind]

Solr will ship a systemd-startscript. It's already commited but will only ship from solr 10.0 onward. It's however so basic that it should simply also work with solr 8 and 9. We could skip relying on the init.d-based shell-skript here and use the systemd-based variant to directly interface with .../bin/solr for start/stop.
https://issues.apache.org/jira/browse/SOLR-14410
Code for systemd-unit at: https://github.com/apache/solr/blob/main/solr/bin/systemd/solr.service

[fraenki]

I'd like to support both, the old-style init.d and systemd service. This way the module could still be used on non-systemd systems.

Is anyone interested to submit a PR? :)