feat(mob): Create boss

[PopsIDX]

🚀 Feature Request

• The game should finish with an island containing a Boss mob instead of mob waves.

📝 Describe the solution

• Create a Boss scene
• The boss should be big and have a lot of HP
• It should have a big health bar at the top of the screen
• It should have a different attack from other mob (maybe a projectile ?)
• On death, it should show a "You win" screen ?
• The last island on the map should spawn a Boss

🤔 Describe alternatives you've considered

• On death, wait for the player to come back to the boat and show a "You win" screen

💡 Additional context

• The boss sprite could be the crab king ?