Align to v0.12.2

[terencechain]

This PR tracks to the progress to align Prysm to v.0.12.2 which is the target version for Medella testnet
https://github.com/ethereum/eth2.0-specs/releases/tag/v0.12.2

Beacon chain ⛓️

• Add DEPOSIT_CHAIN_ID and DEPOSIT_NETWORK_ID to configuration (add deposit chain id and network id to config ethereum/consensus-specs#1988)
• [non-substantive] Compute committee count per slot is epoch based and rewrite gossip condition to be less stateful (Avoid state in p2p validation, compute committee count per slot for epoch ethereum/consensus-specs#1904)
• [non-substantive] Apply strict uint64 casting (Apply strict uint64 casting ethereum/consensus-specs#1746, Proposal: generic uint_to_bytes ethereum/consensus-specs#1935)
• [non-substantive] Separate config files by phases (Separate config files by phases + update phase 1 configs ethereum/consensus-specs#1882)
• [non-substantive] Reorder conditions to validator target_epoch before its use (process_attestation: Validate epoch before using it ethereum/consensus-specs#1996)

Fork choice 🍴

• [bug-fix] Fix edgecase in updating target checkpoint state (Fix store_target_checkpoint_state ethereum/consensus-specs#1886)
• [non-substantive] Use parent_root in ancestor check to add mutations after assertions (Use parent_root for finalized chain check ethereum/consensus-specs#1884)
• [non-substantive] Avoid redundant call to get_ancestor (Fork choice: avoid redundant call to get_ancestor ethereum/consensus-specs#1880)

Validator 🧑‍🤝‍🧑

• [non-substantive] Fix param in epoch_boundary_block_root calculation (Fix epoch_boundary_block_root computation ethereum/consensus-specs#1962)

Networking 🖥️

• Add queuing possibility to p2p messages in gossip (add queueing possibility to p2p messages in gossip ethereum/consensus-specs#1956)
• Update gossipsub config params and add FAQ for explanation of choices (Match gossip v1.1 D_low, extend gossip_history param, add FAQ section ethereum/consensus-specs#1958)
• Remove ssz encoding from req/resp (remove 'ssz' format from req/resp ethereum/consensus-specs#1982) QSP-13 Only Allow Snappy P2P Encoding #6415
• Add gossip conditions that block must have finalized checkpoint as ancestor (add that current block is in the same chain as finalized ancestor ethereum/consensus-specs#1985) Reject a block which its parent is not part of the finalized chain #6549
• [non-substantive] p2p formatting RP ((non-substantive) p2p formating ethereum/consensus-specs#1953)

Spec test

• Update spec tests Update spectests to v0.12.2 #6713

[terencechain]

Completed. We are fully complied with v0.12.2

Thanks @nisdas !

[terencechain]

Closed too early Update gossipsub config params is not yet done