refactor(Core/Motd): Move motd from conf to db (#15111)

data/sql/updates/pending_db_auth/rev_1676759011048897700.sql

@@ -0,0 +1,11 @@
+--
+DROP TABLE IF EXISTS `motd`;
+CREATE TABLE `motd` (
+    `realmid` INT NOT NULL,
+    `text` LONGTEXT NULL DEFAULT NULL,
+    PRIMARY KEY (`realmid`)
+) ENGINE=InnoDB;
+
+DELETE FROM `motd` WHERE  `realmid`=1;
+INSERT INTO `motd` (`realmid`, `text`) VALUES
+(-1, 'Welcome to an AzerothCore server.');