Update BeaconBlockBody with AttestationContainer

[mehdi-aouadi]

PR Description

Update BeaconBlockBody container with AttestationContainer

Fixed Issue(s)

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.

[mehdi-aouadi]

This PR breaks the compilation and introduces incomplete changes. Missing thing:

• Check TODOs
• AggregateAndProof conatiner must be gentrified to handle both Attestation and AttestationElectra (using AttestationContainer like the BeaconBlockBody)
• The json annotated tech.pegasys.teku.api.schema.SignedBeaconBlock and its subclasses should be refactored according to the tech.pegasys.teku.api.schema.BeaconBlockBody hierarchy refcatoring
• Some Attestation casting have been added just to keep things working temporarily and should be removed/reviewed