Adds a config that skews random spawners weights. (#84616)

## About The Pull Request
Title. It's an exponent that multiplies weights of random spawners.
For example, if the exponent were 0.8, and the spawner has a natural
99.9% chance to spawn a donk-pocket and a 0.01% of a vial of
adminodrazine, after calculations it'd be roughly 99.6% vs 0.4%.

## Why It's Good For The Game
This can give admins/keyholders more control over random spawners.
~~However, most of the random spawners are maploaded things so an admin
would've to get to edit the config quite fast before SSatoms initializes
to witness the most out of it, but I'm just ranting.~~

## Changelog

🆑
admin: Added a config that regulares random spawners weights.
/🆑

code/controllers/configuration/entries/game_options.dm

@@ -464,3 +464,12 @@
 /datum/config_entry/number/max_positive_quirks
 	default = 6
 	min_val = -1
+
+/**
+ * A config that skews with the random spawners weights
+ * If the value is lower than 1, it'll tend to even out the odds
+ * If higher than 1, it'll lean toward common spawns even more.
+ */
+/datum/config_entry/number/random_loot_weight_modifier
+	default = 1
+	min_val = 0.05