go: default to RPC 127.0.0.1

[protolambda]

Services all default to binding the RPC to 0.0.0.0 currently. It's considered better to default to 127.0.0.1 to not accidentally expose an RPC publicly, like many L1 clients do. This may break existing configurations, so this change should be coupled to a release, and goes into many releases (op-batcher/op-propoiser/op-challenger/op-node/op-conductor to name a few).