Configurable Block Map for Lightning Transforms Blocks

[GideonWhite1029]

Based on #1422 by @granny.

Replaces hardcoded block transformations with a configurable block-map, allowing server admins to define any block-to-block transformation caused by lightning strikes. The nearby-blocks effect now applies to all blocks defined in the map, not just sand.

gameplay-mechanics:
  lightning-transforms-blocks:
    enabled: true
    nearby-blocks:
      enabled: true
      max-depth: 65
      max-iteration: 65
    block-map:
      minecraft:water: minecraft:stone
      minecraft:sand: minecraft:glass
      minecraft:stone: minecraft:obsidian