metrics: transition all metrics to using metricsgen generated constructors. (#8488)

## What does this change do?

This pull request completes the change to the `metricsgen` metrics. It adds `go generate` directives to all of the files containing the `Metrics` structs.

Using the outputs of `metricsdiff` between these generated metrics and `master`, we can see that there is not a diff between the two sets of metrics when run locally.
```
[william@sidewinder] tendermint[wb/metrics-gen-transition]:. ◆ ./scripts/metricsgen/metricsdiff/metricsdiff metrics_master metrics_generated
[william@sidewinder] tendermint[wb/metrics-gen-transition]:. ◆
```

This change also adds parsing for a `metrics:` key in a field comment. If a comment line begins with `//metrics:` the rest of the line is interpreted to be the metric help text. Additionally, a bug where lists of labels were not properly quoted in the `metricsgen` rendered output was fixed.

scripts/metricsgen/testdata/commented/metrics.gen.go

@@ -18,7 +18,7 @@ func PrometheusMetrics(namespace string, labelsAndValues ...string) *Metrics {
 			Namespace: namespace,
 			Subsystem: MetricsSubsystem,
 			Name:      "field",
-			Help:      "Height of the chain.We expect multi-line comments to parse correctly.",
+			Help:      "Height of the chain. We expect multi-line comments to parse correctly.",
 		}, labels).With(labelsAndValues...),
 	}
 }

scripts/metricsgen/testdata/tags/metrics.gen.go

@@ -19,7 +19,8 @@ func PrometheusMetrics(namespace string, labelsAndValues ...string) *Metrics {
 			Subsystem: MetricsSubsystem,
 			Name:      "with_labels",
 			Help:      "",
-		}, append(labels, "step,time")).With(labelsAndValues...), WithExpBuckets: prometheus.NewHistogramFrom(stdprometheus.HistogramOpts{
+		}, append(labels, "step", "time")).With(labelsAndValues...),
+		WithExpBuckets: prometheus.NewHistogramFrom(stdprometheus.HistogramOpts{
 			Namespace: namespace,
 			Subsystem: MetricsSubsystem,
 			Name:      "with_exp_buckets",