Added Spawn Egg Functionality

[OfficialKris]

Description

Added entities.json and extractor
Added entities registry
Added support for right clicking spawn egg and spawning entity
Added add_mob function in server (very rough, probably can be put into "world")

Kept Entities_Registry Enum as it is used in many places, probably can be substituted for macro

Testing

Tested both block placing and egg spawning
Tested different types of eggs and all worked
Future work for separate PRs:

• Interacting with mobs causes server to kick player because only attacks between players are allowed.
• Unique characteristics are not supported (horses color, slime size)
• Mob ai

Checklist

Things need to be done before this Pull Request can be merged.

• Code is well-formatted and adheres to project style guidelines: cargo fmt
• Code does not produce any clippy warnings: cargo clippy
• All unit tests pass: cargo test
• I added new unit tests, so other people don't accidentally break my code by changing other parts of the codebase. How?