Rayonism Teku Sharding modifications
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- [x] Add new/modify existing SSZ structures
- [x] Implement block/epoch transition logic
- [x] Add sanity transtion tests
- [x] Add gossip `shard_header` topic with validation
- [x] Add beacon block proposer logic to include `shard_header`s from the gossip topic
- [x] Add beacon attester logic to 'vote' for a shard header
(no actual attestation logic: just get first non-empty header if any)
- [x] Add `shard_blob_{shard}` topic 'router' which just directly expose this topic via REST API for a 'Shard Blob Node'
_Gossip message validation is performed on the 'Shard Blob Node' side?_
- [ ] Add REST API for `ShardBlob` publishing for a 'Shard Blob Node'
- [ ] Add REST API for `ShardBlob` confirmation progress in the `BeaconState`