adds recording who deleted a note (#50445)

It came up that this isn't recorded, only logged.

Technically needs syncing merge with schema change but only deleting notes would break from this and tbh that isn't done very often so I think it'd be fine to yolo.

SQL/tgstation_schema_prefixed.sql

@@ -258,6 +258,7 @@ CREATE TABLE `SS13_messages` (
   `lasteditor` varchar(32) DEFAULT NULL,
   `edits` text,
   `deleted` tinyint(1) unsigned NOT NULL DEFAULT '0',
+  `deleted_ckey` VARCHAR(32) NULL DEFAULT NULL,
   PRIMARY KEY (`id`),
   KEY `idx_msg_ckey_time` (`targetckey`,`timestamp`, `deleted`),
   KEY `idx_msg_type_ckeys_time` (`type`,`targetckey`,`adminckey`,`timestamp`, `deleted`),