Allow end obsidian pillar generation to be customised with datapacks

Currently, end obsidian pillar generation is hardcoded. It could be made so the end pillar generation could be customised with data packs.

Values:

• Shape: This controls the shape of the pillar. It can be square or circle. A square pillar will have its outer edges cut off until it becomes a square, similar to old versions. A circle end obsidian pillar uses the current circle shape. The circle value is used by default.
• Base block: This is obsidian by default. This determines the base block of the end obsidian pillar.
• End crystal base: This determines whether the end crystal has extra visual bedrock or not. The value is true by default.
• End crystal block: This determines the block the end crystal lies on. Defaults to bedrock.
• End crystal offset: This is where the end crystal's position may be off-centered from the end crystal block. Defaults to 0, 1, 0 in Minecraft coordinates, using relative block position.
• End crystal block offset: This is where the block the end crystal lies on may be off-centered from the top of the center base block of the end obsidian pillar. Defaults to 0, 1, 0 in Minecraft coordinates, using relative block position.
• Starting height: This is where the height the end obsidian pillar starts at. Defaults to 0.
• Height: This is how tall the end obsidian pillar will be, starting from the starting height. 
• Radius: This determines the distance between the center and the boundary of the end obsidian pillar. Value must be at least 1.
• Fire overrides block: This controls whether the spawning end crystal's fire can override any block. False by default.
• End pillar cage: This controls whether the obsidian end pillar uses a cage or not.
• End pillar cage block: This controls the block the end pillar cage uses. Defaults to iron bars.
• End pillar cage faces: These determine the faces the end pillar cage which can generate. Defaults to up, east, west, south and north.
• Hollow end pillar: If true, the end pillar is hollow.
• Hollow end pillar block: The block to fill the hollow end pillar if enabled. Defaults to air.
• Integrity: This controls the chance each end pillar block generates. Defaults to 1.0, meaning 100% chance. Value must be between 0.0 and 1.0 inclusive.