Add ShellCheck's --enable=all inside cmd/

The only exception is `cmd/vdev_id/vdev_id` which might be a subject of
refactoring (see #12084)

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Signed-off-by: szubersk <szuberskidamian@gmail.com>
Closes #12912

cmd/zed/zed.d/Makefile.am

@@ -10,6 +10,10 @@ dist_zedconf_DATA = \
 	zed-functions.sh \
 	zed.rc
 
+SHELLCHECKSCRIPTS = zed-functions.sh zed.rc
+SHELLCHECK_OPTS = --enable=all
+SHELLCHECK_SHELL = dash
+
 zedexecdir = $(zfsexecdir)/zed.d
 
 dist_zedexec_SCRIPTS = \