fix: restore P2P bootnodes for base-consensus

Add BASE_NODE_P2P_BOOTNODES to .env.mainnet and .env.sepolia with
the same ENR bootnode records previously under OP_NODE_P2P_BOOTNODES.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>