This pull request adds an additional set of metrics targeted at providing more visibility into `abci++`.

The following set of metrics are added and exposed through the `metrics` endpoint:

```
tendermint_consensus_proposal_receive_count{chain_id="test-chain-IrF74Y",status="accepted"} 34
tendermint_consensus_proposal_create_count{chain_id="test-chain-IrF74Y"} 34
tendermint_consensus_vote_extension_receive_count{chain_id="test-chain-IrF74Y",status="accepted"} 34
tendermint_consensus_round_voting_power_percent{chain_id="test-chain-IrF74Y",vote_type="precommit"} 1
tendermint_consensus_round_voting_power_percent{chain_id="test-chain-IrF74Y",vote_type="prevote"} 1
tendermint_state_consensus_param_updates{chain_id="test-chain-IrF74Y"} 0
tendermint_state_validator_set_updates{chain_id="test-chain-IrF74Y"} 0
tendermint_consensus_late_votes{chain_id="test-chain-IrF74Y",vote_type="precommit"} 16
```

This pull request also updates the `metrics.md` file to include some metrics that were previously missed. My hope is to generate the `metrics.md` file with a future version of the tool being architected in #8479