content: Document the protocol-level details of Gnosis Chain

We need clearer protocol specs for Gnosis Chain that articulate the precise technical differences from Ethereum

- e.g. Block rewards contract
- e.g. SBC contract for validators
- e.g. future changes to Transaction Relays, Block Builders/Relays

We can drop most of the AuRa documentation that is no longer within the chain and focus only on still-existent changes