Icinga v 2.13.3

New version:

• Icinga v2.13.3 #8 (closed)
• Added option to control database cleanup (default retention set to 2 years) #6 (closed)
• Added check_apache_status, check_nginx_status check_postgres and eapol_test #5 (closed)
• Support InfluxDB2 #7 (closed)
• Add libfile-slurp-perl (fixes check_nwc_health) #9 (closed)
• Removed gateway from docker-compose example #4 (closed)