Block processing detailed metrics

[dapplion]

Add more detailed metrics for block processing. From #2468

Originally inspired in May 2021 from here
https://github.com/sigp/lighthouse/blob/stable/beacon_node/beacon_chain/src/metrics.rs

• beacon_block_processing_requests_total: Count of blocks submitted for processing
• beacon_block_processing_successes_total: Count of blocks processed without error
• beacon_block_processing_seconds: Full runtime of block processing
• beacon_block_processing_block_root_seconds: Time spent calculating the block root when processing a block.
• beacon_block_processing_db_read_seconds: Time spent loading block and state from DB for block processing
• beacon_block_processing_catch_up_state_seconds: Time spent skipping slots on a state before processing a block.
• beacon_block_processing_committee_building_seconds: Time spent building/obtaining committees for block processing.
• beacon_block_processing_signature_seconds: Time spent doing signature verification for a block.
• beacon_block_processing_core_seconds: Time spent doing the core per_block_processing state processing.
• beacon_block_processing_state_root_seconds: Time spent calculating the state root when processing a block.
• beacon_block_processing_db_write_seconds: Time spent writing a newly processed block and state to DB
• beacon_block_processing_attestation_observation_seconds: Time spent hashing and remembering all the attestations in the block