Implement basic validator data column custody

[jimmygchen]

Description

Implement spec: ethereum/consensus-specs#3871

This isn't mandatory for peerdas-devnet-4, but the change is compatible with the devnet - it means potentially storing more columns when running a node with validators. The spec hasn't been merged yet but client teams have started looking into this. We could either wait for the spec to be merged or implement this behind a CLI flag for testing purpose until the spec change is merged.

Tasks

Following the design in https://hackmd.io/@dapplion/validator_custody_no_backfill

• make all codepaths read the CGC from a Mutex,
• carefully persist new consistency data to disk

cgc_updates: Vec<(Slot, u64)>,
backfilled_cgc: (Slot, u64),

• restart the backfill under certain conditions
• update gossip subscriptions
• cache the to-advertise CGC somewhere and update ENR + status at that moment