Verifiable Randomness Function

Unfortunately at the moment there is no way to generate randomness using ink! The available options are:

• Creating a VRF oracle contract that will generate randomness.
  • (DIA is working on it for Astar.)
• On the runtime level, adding a Chain Extension to the RandomnessCollectiveFlip pallet so it's accessible within ink! contracts.
  • Astar team is working on this.
• Add a function in the ink_env to retrieve the current and previous block hashes, on which to base randomness.