[EIP-7549] Move committee index outside attestation

[lucassaldanha]

Description

Move the committee index field outside of the signed Attestation message to allow aggregation of equal consensus votes.

References

• EIP-7549
• Consensus Spec PR
• Updated Consensus Spec

Tasks

• Refactor get_attesting_indices #8089 Refactor get_attesting_indices
• Update the attestations containers #8026 Add/update attestations containers
• Update indexed attestation containers #8123 Add/update index attestations containers
• Update phase0 attestations processing logic #8031 Update the attestation processing
• Flatten aggregation bits #8156 Flattern aggregation bits
• Update preset values #8103 Update preset values
• Update beacon block body Electra #8130 Update beacon block body

Once the previous done, we can start merging the changes in master while progressing on the following:

• Update attestation construction #8101 Update attestation production
• Update attestation aggregation logic #8027 Update attestation aggregation logic
  Replace committee bits with committee indices #8270 Replace committee_bits with committee_indices
• Update p2p aggregation gossip topic  #8099 Update the aggregation gossip topic
• Update the attestation gossip topic #8100 Update the attestation gossip topic
• Move committee_bits property to the end #8340 Move committee_bits property to the end
• Add the attestations pool v2 API #8029 Add the GetAttestations v2 APIs (attestations pool)
• Add the new PostAttestation v2 API #8424 Add the PostAttestation v2 APIs (attestations pool)
• Add the block attestations v2 API #8264 Add the GetBlockAttestations v2 APIs (block's attestations)
• Add the new GetAttesterSlashing v2 API #8122 Add the GetAttesterSlashings v2 API (get attester slashing)
• Add the new PostAttesterSlashing V2 API #8425 Add the PostAttesterSlashing v2 API (post attester slashing)
• Add the new GetAggregateAttestation V2 API #8420 Add the GetAggregateAttestation v2 API
• [beacon api] [electra] Add publishAggregateAndProofsV2 to support EIP-7549 #8439 Add the PostAggregateAttestation v2 API

Tech debt:

• ELECTRA milestone over AggregateAttestationValidatorTest and implement ElectraAttestationValidatorTest

Possible evolutions

• Separate type for on-chain attestation aggregates #8554 Separate type for on-chain attestation aggregates
• Separate type for unaggregated network attestations #8555 Separate type for unaggregated network attestations