sysutils/graylog: update to 4.0.8

ChangeLog: https://docs.graylog.org/en/4.0/pages/changelog.html#graylog-4-0-8

Submitted by: Charles Gonçalves <charles@freebsdbrasil.com.br>
Sponsored by: SkunkWerks, GmbH
Sponsored by FreeBSD Brasil
Differential Revision: https://reviews.freebsd.org/D30666