Persist light client updates

[eserilev]

Issue Addressed

Partially #3651

Proposed Changes

This PR aims to persist light client updates. Once persisted, this will allow lighthouse nodes to serve them over RPC.

[eserilev]

This should be ready for another review! in the meantime i started on work to persist light client bootstraps based on the strategy detailed in this doc written by lion: https://hackmd.io/@dapplion/BkxPbc6eQT

[dapplion]

Chatted with @michaelsproul offline, and we agree to put this data on the hot db, so this PR is good to go

[dapplion]

Same CI failures

FAIL [   4.186s] beacon_chain::beacon_chain_tests store_tests::light_client_updates_test

FAIL [   1.187s] ef_tests::tests light_client_update

And the basic simulator

[eserilev]

Since the fork epoch boundaries in basic-sim aren't multiples of 256, the light client periods dont align with the fork boundaries. We end up getting some BeaconStateError::IncorrectStateVariant when constructing light client updates

I've gotten the basic-sim tests to pass by moving the light client update logic to the bottom of recompute_and_cache_updates. This prevents the light client update stuff from affecting optimistic and finality update

I've also completely removed any checks related to light client updates in basic-sim. I've kept the test vectors related to optimistic and finality updates. I think we have enough light client update test coverage in other places to live with this for now...

[jimmygchen]

@mergify queue

[mergify[bot]]

queue

✅ The pull request has been merged automatically

The pull request has been merged automatically at 3913ea44c6dc412c6e723383dd398264a967faf3