Detect invalid proposer signature on RPC block processing (#6519)

Complements
- https://github.com/sigp/lighthouse/pull/6321

by detecting if the proposer signature is valid or not during RPC block processing. In lookup sync, if the invalid signature signature is the proposer signature, it's not deterministic on the block root. So we should only penalize the sending peer and retry. Otherwise, if it's on the body we should drop the lookup and penalize all peers that claim to have imported the block

beacon_node/beacon_chain/src/lib.rs

@@ -78,7 +78,7 @@ pub use beacon_fork_choice_store::{BeaconForkChoiceStore, Error as ForkChoiceSto
 pub use block_verification::{
     build_blob_data_column_sidecars, get_block_root, BlockError, ExecutionPayloadError,
     ExecutionPendingBlock, GossipVerifiedBlock, IntoExecutionPendingBlock, IntoGossipVerifiedBlock,
-    PayloadVerificationOutcome, PayloadVerificationStatus,
+    InvalidSignature, PayloadVerificationOutcome, PayloadVerificationStatus,
 };
 pub use block_verification_types::AvailabilityPendingExecutedBlock;
 pub use block_verification_types::ExecutedBlock;