Add gold value to Convertibles

[vsong]

Implement a script to insert and update gold values for convertible items from Markethunt API, as well as updating Convertibles webpage to display gold/sb value statistics.

Additional admin steps needed after deployment:

1. Run the following migration script in converter database:

   CREATE TABLE `item_markethunt` (
   `item_id` int NOT NULL,
   `gold_value` bigint DEFAULT NULL,
   `sb_value` double DEFAULT NULL,
   PRIMARY KEY (`item_id`)
   ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
   -- set 1 Gold equal to 1 Gold. Do not set to 0, or the MH economy will collapse!
   INSERT INTO item_values (item_id, gold_value) VALUES(431, 1);

2. Add insert_gold_values.php to the daily cron. Markethunt refreshes its data at 12:05am UTC, I recommend running the cron at 12:15am UTC.
3. Copy new config.php variables from config.php.example

Preview of UI changes:

[vsong]

Updated PR summary with new table name