## What does this pull request do?
This pull requests adds two metrics intended for use in calculating an experimental value for `MessageDelay`.
The metrics are as follows:
```
# HELP tendermint_consensus_complete_prevote_message_delay Difference in seconds between the proposal timestamp and the timestamp of the prevote that achieved 100% of the voting power in the prevote step.
# TYPE tendermint_consensus_complete_prevote_message_delay gauge
tendermint_consensus_complete_prevote_message_delay{chain_id="test-chain-aZbwF1"} 0.013025505
# HELP tendermint_consensus_quorum_prevote_message_delay Difference in seconds between the proposal timestamp and the timestamp of the prevote that achieved a quorum in the prevote step.
# TYPE tendermint_consensus_quorum_prevote_message_delay gauge
tendermint_consensus_quorum_prevote_message_delay{chain_id="test-chain-aZbwF1"} 0.013025505
```
## Why this change?
For more information on what these metrics are calculating, see #7202. The aim is to merge to backport these metrics to v0.34 and run nodes on a few popular chains with these metrics to determine the experimental values for `MessageDelay` on these popular chains and use these to select our default `SynchronyParams.MessageDelay` value.
## Why Gauges for the metrics?
Gauges allow us to overwrite the metric on each successive observation. We can then capture these metrics over time to track the highest and lowest observed value.
William Banfield
0c82ceaa5f