MDEV-40377 Change Server source code to point to new docs (12.3 part)

Replace the remaining Knowledge Base links with their MariaDB
Documentation equivalents, including the 838 URLs in the help tables.
Only URLs change in fill_help_tables.sql.

Merging upward: fill_help_tables.sql conflicts at 10.11->11.4 and
11.8->12.3. At those two merges keep the target branch's version,
since 11.4, 11.8 and 12.3 each carry their own URL fix. From 12.3 to
13.1 and 13.1 to main it merges cleanly; take the incoming change.
.github/pull_request_template.md is deleted in 12.3; keep the deletion.

Author: KhaledR57

debian/additions/mariadb.conf.d/60-galera.cnf

@@ -2,8 +2,8 @@
 # * Galera-related settings
 #
 # See the examples of server wsrep.cnf files in /usr/share/mariadb and read
-# more at https://mariadb.com/kb/en/galera-cluster/ and
-# https://mariadb.com/kb/en/configuring-mariadb-galera-cluster/
+# more at https://mariadb.com/docs/galera-cluster and
+# https://mariadb.com/docs/galera-cluster/galera-management/configuration/configuring-mariadb-galera-cluster
 
 [galera]
 #wsrep_cluster_name       = "MariaDB Galera Cluster"