MDEV-30837: Remove usage of AWK from Debian init and postinst scripts

AWK in used in Debian SysV-init and postinst scripts to determine
is there enough space starting MariaDB database or create new
database to target destination.

These AWK scripts can be rewrited to use pure SH or help
using Coreutils which is mandatory for usage of MariaDB currently.

Reasoning behind this is to get rid of one very less used dependency

debian/mariadb-server-10.6.mariadb.init

@@ -84,7 +84,10 @@ sanity_checks() {
 
   # check for diskspace shortage
   datadir=`mariadbd_get_param datadir`
-  if LC_ALL=C BLOCKSIZE= df --portability $datadir/. | tail -n 1 | awk '{ exit ($4>4096) }'; then
+  # As preset blocksize of GNU df is 1024 then available bytes is $df_available_blocks * 1024
+  # 4096 blocks is then lower than 4 MB
+  df_available_blocks=`LC_ALL=C BLOCKSIZE= df --output=avail "$datadir" | tail -n 1`
+  if [ "$df_available_blocks" -lt "4096" ]; then
     log_failure_msg "$0: ERROR: The partition with $datadir is too full!"
     echo                "ERROR: The partition with $datadir is too full!" | $ERR_LOGGER
     exit 1

debian/mariadb-server-10.6.preinst

@@ -209,8 +209,10 @@ if [ ! -d $mysql_datadir ] && [ ! -L $mysql_datadir ]; then
   mkdir -Z $mysql_datadir
 fi
 
-# checking disc space
-if LC_ALL=C BLOCKSIZE= df --portability $mysql_datadir/. | tail -n 1 | awk '{ exit ($4>1000) }'; then
+# As preset blocksize of GNU df is 1024 then available bytes is $df_available_blocks * 1024
+# 4096 blocks is then lower than 4 MB
+df_available_blocks=`LC_ALL=C BLOCKSIZE= df --output=avail "$datadir" | tail -n 1`
+if [ "$df_available_blocks" -lt "4096" ]; then
   echo "ERROR: There's not enough space in $mysql_datadir/" 1>&2
   db_stop
   exit 1