/bin/systemctl: No such file or directory

[Klemart3D]

With DSM 6.2.4-25556 Update 5 on DS215j & DS216j Synology NAS:

1. To don't have following error: /bin/systemctl: No such file or directory
   I replaced line 61 by: synoservice --restart pkgctl-Plex\ Media\ Server
   This command can also be used:
   sh /var/packages/Plex\ Media\ Server/scripts/start-stop-status stop && sh /var/packages/Plex\ Media\ Server/scripts/start-stop-status start

2. To don't have following error: Error opening Certificate /usr/syno/etc/certificate/system/default/RSA-cert.pem
   I have to replace all RSA-cert.pem by cert.pem, so I add it as a variable. See my version of script:
   https://gist.github.com/Klemart3D/a33765d2ead0b56fcdfdccf9334a4d20#file-plex-ssl-certificate-sh
   NB: I also pass domain name as variable to don't have to edit the script file on each NAS.