allow filtering block processor logs by topic (#5321)

Add separate log topic for `block_processor` messages.

Topic named similar to the other `_processor` modules:

- `eth2_processor` --> `gossip_eth2`
- `light_client_processor` --> `gossip_lc`
- `optimistic_processor` --> `gossip_opt`

beacon_chain/gossip_processing/block_processor.nim

@@ -38,6 +38,8 @@ from ../spec/state_transition_block import validate_blobs
 
 export sszdump, signatures_batch
 
+logScope: topics = "gossip_blocks"
+
 # Block Processor
 # ------------------------------------------------------------------------------
 # The block processor moves blocks from "Incoming" to "Consensus verified"