docs: add missing metrics (#5325)

## Description

Add missing metrics. 

`Blockchain/v2` exposes metrics for events. I don't find these as something a node operator should utilize as it does not bring insight. 

Closes: #XXX

consensus/metrics.go

@@ -138,14 +138,12 @@ func PrometheusMetrics(namespace string, labelsAndValues ...string) *Metrics {
 			Name:      "byzantine_validators_power",
 			Help:      "Total power of the byzantine validators.",
 		}, labels).With(labelsAndValues...),
-
 		BlockIntervalSeconds: prometheus.NewGaugeFrom(stdprometheus.GaugeOpts{
 			Namespace: namespace,
 			Subsystem: MetricsSubsystem,
 			Name:      "block_interval_seconds",
 			Help:      "Time between this and the last block.",
 		}, labels).With(labelsAndValues...),
-
 		NumTxs: prometheus.NewGaugeFrom(stdprometheus.GaugeOpts{
 			Namespace: namespace,
 			Subsystem: MetricsSubsystem,

docs/tendermint-core/metrics.md

@@ -37,6 +37,7 @@ The following metrics are available:
 | consensus_block_parts                  | counter   | peer_id       | number of blockparts transmitted by peer                               |
 | consensus_latest_block_height          | gauge     |               | /status sync_info number                                               |
 | consensus_fast_syncing                 | gauge     |               | either 0 (not fast syncing) or 1 (syncing)                             |
+| consensus_state_syncing                | gauge     |               | either 0 (not state syncing) or 1 (syncing)                            |
 | consensus_block_size_bytes             | Gauge     |               | Block size in bytes                                                    |
 | p2p_peers                              | Gauge     |               | Number of peers node's connected to                                    |
 | p2p_peer_receive_bytes_total           | counter   | peer_id, chID | number of bytes per channel received from a given peer                 |