datasource: Fortinet STIX

[MaineK00n]

https://www.fortiguard.com/psirt/FG-IR-25-254

[MaineK00n]

https://oasis-open.github.io/cti-documentation/stix/intro.html
https://docs.oasis-open.org/cti/stix/v2.1/os/stix-v2.1-os.html