Gloas: track head envelope in `canonical_head`

[michaelsproul]

Description

We probably want to track the head payload (if there is one) inside the canonical head tracker. Might make sense to do this once we have fork choice.

[michaelsproul]

Complete in:

• Gloas spec v1.7.0-alpha.5 and beacon_chain tests #8998

lighthouse/beacon_node/beacon_chain/src/canonical_head.rs

Lines 721 to 726 in cf3d5e2

	BeaconSnapshot {
	beacon_block: Arc::new(beacon_block),
	execution_envelope,
	beacon_block_root: new_view.head_block_root,
	beacon_state,
	}