etna: e2e guide ERC20 on C-chain -> ERC20 PoS L1 (decoupling gas)

[owenwahlgren]

Write an e2e guide for Etna upgrade.

• Deploy ERC20 on C-Chain
• Deploy a new L1 as PoA (registering to P-Chain)
• ICTT transfer the ERC20 to new L1 as ERC20 (decoupling gas and staking token)
• Upgrade PoA -> PoS (using the bridged ERC20 and upgrading the proxy)