dtrace.1: Document security.bsd.allow_destructive_dtrace
PR: 288284
Reviewed by: bcr, markj
MFC after: 3 days
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D51633
(cherry picked from commit 1acfb873cf2e59f9ddf53602cbc67fa810c878a6)