* op-node: Execution Layer Sync

This passes unsafe payloads directly the EngineController for immediate
insertion when Execution Layer sync is active. This tells the execution
client to sync to that target. Once the EL sync is complete, the last
unsafe payload is marked as safe. This is required when doing snap sync
because the EL does not have the pre-state required to do the engine
consolidation until the sync is complete.

* op-e2e: Snap Sync action test

* op-e2e: Actually run TestSystemE2E

* op-service/node: Add time.Since to Clock & use it