autoconf: use include directives instead of recursing down cmd

No installation diff, dist lost
  -zfs-2.1.99/cmd/fsck_zfs/fsck.zfs
which was distributed erroneously, since it's generated

Also clean gitrev on clean

Also add -e 'any possible bashisms' to default checkbashisms flags,
and fully parallelise it and shellcheck, and it works out-of-tree, too

Also align the Release in the dist META file correctly

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes openzfs#13316

contrib/bpftrace/Makefile.am

@@ -1,3 +1,3 @@
 dist_noinst_DATA += %D%/taskqlatency.bt %D%/zfs-trace.sh
 
-SHELLCHECKSCRIPTS += %D%/zfs-trace.sh
+SHELLCHECKSCRIPTS += %D%/zfs-trace.sh