Add zilstat script to report zil kstats in a user friendly manner

Added a python script to process both global and per dataset
zil kstats and report them in a user friendly manner similar
to arcstat and dbufstat.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Richard Elling <Richard.Elling@RichardElling.com>
Signed-off-by: Ameer Hamza <ahamza@ixsystems.com>
Closes #13704

rpm/generic/zfs.spec.in

@@ -409,7 +409,8 @@ make install DESTDIR=%{?buildroot}
 find %{?buildroot}%{_libdir} -name '*.la' -exec rm -f {} \;
 %if 0%{!?__brp_mangle_shebangs:1}
 find %{?buildroot}%{_bindir} \
-    \( -name arc_summary -or -name arcstat -or -name dbufstat \) \
+    \( -name arc_summary -or -name arcstat -or -name dbufstat \
+    -or -name zilstat \) \
     -exec %{__sed} -i 's|^#!.*|#!%{__python}|' {} \;
 find %{?buildroot}%{_datadir} \
     \( -name test-runner.py -or -name zts-report.py \) \
@@ -487,6 +488,7 @@ systemctl --system daemon-reload >/dev/null || true
 %{_bindir}/arc_summary
 %{_bindir}/arcstat
 %{_bindir}/dbufstat
+%{_bindir}/zilstat
 # Man pages
 %{_mandir}/man1/*
 %{_mandir}/man4/*