feat: implement pipeline BackfillSync

[fgimenez]

Closes #9012

Changes from

reth/crates/consensus/beacon/src/engine/sync.rs

Lines 35 to 39 in 83cbcb9

	pub(crate) struct EngineSyncController<DB, Client>
	where
	DB: Database,
	Client: HeadersClient + BodiesClient,
	{

to implement BackfillSync, there's also a new BackfillEvent variant to capture and log dropped tasks.

[mattsse]

very nice, one more puzzle piece