Add index on playerbots_random_bots to reduce deadlocks (#1247)

This commit adds a missing composite index on the `playerbots_random_bots` table
(`owner`, `bot`, `event`) to improve database performance during high playerbot
activity.

Adding this index significantly reduces the occurrence of deadlocks when multiple
threads access the random bots table simultaneously.

The change is 100% backward-compatible and does not affect existing data or
functionality.

data/sql/playerbots/updates/db_playerbots/2025_04_26.sql

@@ -0,0 +1,9 @@
+-- ##########################################################
+-- # Playerbots RandomBots Performance Update
+-- # Add missing index to reduce Deadlocks
+-- # Author: Raz0r1337 aka St0ny
+-- # Date: 2025-04-26
+-- ##########################################################
+
+ALTER TABLE `playerbots_random_bots`
+ADD INDEX `idx_owner_bot_event` (`owner`, `bot`, `event`);