CI: add FreeBSD build with Cirrus CI

As a first step for automatic FreeBSD testing add a build and install
for FreeBSD versions 12.4, 13.2 and 14-snapshot using Cirrus CI.

Reviewed-by: Jose Luis Duran 
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Martin Matuska <mm@FreeBSD.org>
Closes #15332

.gitignore

@@ -42,6 +42,7 @@
 !udev/**
 
 !.editorconfig
+!.cirrus.yml
 !.gitignore
 !.gitmodules
 !AUTHORS
@@ -60,7 +61,6 @@
 !TEST
 !zfs.release.in
 
-
 #
 # Normal rules
 #