metrics: pull library and introduce ResettingTimer and InfluxDB reporter (#15910)

* go-metrics: fork library and introduce ResettingTimer and InfluxDB reporter.

* vendor: change nonsense/go-metrics to ethersphere/go-metrics

* go-metrics: add tests. move ResettingTimer logic from reporter to type.

* all, metrics: pull in metrics package in go-ethereum

* metrics/test: make sure metrics are enabled for tests

* metrics: apply gosimple rules

* metrics/exp, internal/debug: init expvar endpoint when starting pprof server

* internal/debug: tiny comment formatting fix

vendor/github.com/influxdata/influxdb/pkg/escape/strings.go

@@ -0,0 +1,21 @@
+package escape
+
+import "strings"
+
+var (
+	escaper   = strings.NewReplacer(`,`, `\,`, `"`, `\"`, ` `, `\ `, `=`, `\=`)
+	unescaper = strings.NewReplacer(`\,`, `,`, `\"`, `"`, `\ `, ` `, `\=`, `=`)
+)
+
+// UnescapeString returns unescaped version of in.
+func UnescapeString(in string) string {
+	if strings.IndexByte(in, '\\') == -1 {
+		return in
+	}
+	return unescaper.Replace(in)
+}
+
+// String returns the escaped version of in.
+func String(in string) string {
+	return escaper.Replace(in)
+}