Substrate: Use secure randomness

[cernicc]

We are currently using the insecure randomness on chain. The reason was faster implementation because if we wanted to use the more secure random algorithm we would also have to switch to BABE consensus algorithm at the time.

This ticket requires you to use the more secure randomness.

Blocked by:

• Substrate: Switch to BABE consensus algorithm #457

Some more resources:

• https://docs.substrate.io/build/randomness/

[th7nder]

Moonbeam is using randomness from the RelayChain -> https://github.com/moonbeam-foundation/moonbeam/blob/6e6bb1cc21343aa7231b6574091d022138c04108/runtime/moonbeam/src/lib.rs#L1301.
And they're using pallet-parachain-staking, so don't need to use BABE in the parachain.

About pallet-drand, there is a discussion and comparing it to Moonbeam as well: https://kusama.polkassembly.io/post/2645.