MDEV-32336 deb default config - use uca1400_ai_ci for utf8mb4

utf8mb4_general_ci has been outdated for a while and contained loosely
standardized collations.

UCA-14.0.0 has a more defined collation with multiple benefit that new
users may not immediately consider, or may assume to be default.

By defining default collation for utf8mb4 to be uc1400_ai_ci newly
created tables will have a modern standard collation.

debian/additions/mariadb.conf.d/50-server.cnf

@@ -84,10 +84,10 @@ expire_logs_days        = 10
 # * Character sets
 #
 
-# MySQL/MariaDB default is Latin1, but in Debian we rather default to the full
+# MariaDB default is Latin1, but in Debian we rather default to the full
 # utf8 4-byte character set. See also client.cnf
-character-set-server  = utf8mb4
-collation-server      = utf8mb4_general_ci
+character-set-server     = utf8mb4
+character-set-collations = utf8mb4=uca1400_ai_ci
 
 #
 # * InnoDB