EIP-7002: Execution Layer Validator Exits

[lucassaldanha]

Creating this ticket as a placeholder for all EIP-7002 related work.

Reference: https://eips.ethereum.org/EIPS/eip-7002

Initial take on some tasks:

• Update BlockBody with exits (EIP-7002: Add exits/exits_root to block/block_header #6801)
• Update BlockHeader with exits_root (EIP-7002: Add exits/exits_root to block/block_header #6801)
• Update engine_getPayloadV4 and engine_newPayloadV4 to include exits in the Execution Payload. (EIP-7002: Add exits/exits_root to block/block_header #6801)
• Implement Validator Exit contract helper (EIP-7002 - Implement Validator Exit contract helper #6881)
• Update BlockCreator and related block creation logic to include exits from precompiled contract (EIP-7002 - Update BlockCreator and related block creation logic to include exits from precompiled contract #6882)
• Implement Validator Exit Contract system call EIP-7002: Implement Validator Exit Contract system call #6918
• Update exits to be rendered as a "request" per EIP-7685

[lucassaldanha]

I am working on the recent updates on EIP-7002 (exits -> withdrawal request). After that I am going to have to step aside as we have pressing matters in Teku that I need to help with.

I am going to leave this feature in a working state, however I would consider it an experimental implementation until we implement #6918.

@Gabriel-Trintinalia and I have had a few meetings re the missing piece (system calls) so he can help briefing anyone. I am also always available if needed.