add electra attestation container

[mehdi-aouadi]

PR Description

Add Electra attestation containers:

• AttestationElectra
• AttestationElectraSchema

class Attestation(Container):
     aggregation_bits: List[Bitlist[MAX_VALIDATORS_PER_COMMITTEE], MAX_COMMITTEES_PER_SLOT]  # [Modified in EIP7549]
     data: AttestationData
     committee_bits: Bitvector[MAX_COMMITTEES_PER_SLOT]  # [New in EIP7549]
     signature: BLSSignature

Add corresponding property tests and random data generation.

Fixed Issue(s)

fixes Consensys#8026

Documentation

• I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.