add Leap 15.6 publish_distro config

[lkocman]

copy and bump from 15.5

tested on pontifex (had to create bunch of missing toplevel dirs)

mirror@pontifex2:~/openSUSE-release-tools> ./publish_distro publish_distro_conf/publish_leap156_live.config 
GNOME-Live-x86_64 with * doesn't exist, skipping isos
nothing to do

mirror@pontifex2:~/openSUSE-release-tools> ./publish_distro publish_distro_conf/publish_leap156_appliances.config
current 
========== --delete-after ===========
building file list ... done
.d..t...... ./
.d..t...... iso/
total: matches=0  hash_hits=0  false_alarms=0 data=0
deleting in .

sent 136 bytes  received 91 bytes  454.00 bytes/sec
total size is 9  speedup is 0.04
mirror@pontifex2:~/openSUSE-release-tools> ./publish_distro publish_distro_conf/publish_leap156.config 
DVD-x86_64 with [0123456789]*.[0123456789]* doesn't exist, skipping isos
nothing to do

this s being executed by cron under ~mirror

diff --git a/bin/publish_factory_leap b/bin/publish_factory_leap
index ebc645d..7a80d9c 100755
--- a/bin/publish_factory_leap
+++ b/bin/publish_factory_leap
@@ -16,6 +16,12 @@ withlock -q /home/mirror/var/run/withlock/LOCK-publish $PUBLISH_DISTRO $CONF_DIR
 withlock -q /home/mirror/var/run/withlock/LOCK-publish $PUBLISH_DISTRO $CONF_DIR/publish_leap-micro54.config
 withlock -q /home/mirror/var/run/withlock/LOCK-publish $PUBLISH_DISTRO $CONF_DIR/publish_leap-micro54_appliances.config --force

+### 15.6
+
+withlock -q /home/mirror/var/run/withlock/LOCK-publish $PUBLISH_DISTRO $CONF_DIR/publish_leap156.config
+withlock -q /home/mirror/var/run/withlock/LOCK-publish $PUBLISH_DISTRO $CONF_DIR/publish_leap156_live.config
+withlock -q /home/mirror/var/run/withlock/LOCK-publish $PUBLISH_DISTRO $CONF_DIR/publish_leap156_appliances.config --force
+
 ### 15.5

 withlock -q /home/mirror/var/run/withlock/LOCK-publish $PUBLISH_DISTRO $CONF_DIR/publish_leap155.config
lines 1-17/17 (END)

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (03a7aaa) 28.48% compared to head (b506429) 28.48%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #3007 +/- ## ======================================= Coverage 28.48% 28.48% ======================================= Files 85 85 Lines 14717 14717 ======================================= Hits 4192 4192 Misses 10525 10525 ```

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[lkocman]

The failed linter check is unrelated