feat: (light client)add new consensus types for Electra

[rupam-04]

What type of PR is this?

Feature

What does this PR do? Why is it needed?

Adds new consensus types for Electra. This is necessary as depth of sync committee branch changed from 5 in Deneb to 6 in Electra.

• Introduces a new LightClientBootstrapElectra proto struct with depth of sync committee branch set to 6
• Introduces a new LightClientUpdateElectra proto struct with depth of sync committee branch set to 6
• Introduces a new bootstrapElectra struct in consensus-types with currentSyncCommitteeBranch set to interfaces.LightClientSyncCommitteeBranchElectra
• Adds LightClientBootstrapElectra and LightClientUpdateElectra to BUILD.bazel to update SSZ methods
• Introduces a new updateElectra struct in consensus-types with nextSyncCommitteeBranch set to interfaces.LightClientSyncCommitteeBranchElectra
• Adds NextSyncCommitteeBranchElectra() to LightClientBootstrap and LightClientUpdate interfaces

Which issues(s) does this PR fix?

Needed for #12991

Other notes for review

Acknowledgements

• I have read CONTRIBUTING.md.
• I have made an appropriate entry to CHANGELOG.md.
• I have added a description to this PR with sufficient context for reviewers to understand this PR.