Fix unused libbeat.config.module metrics

These metrics existed in the code but were unused and hence always 0.

"libbeat":{"config":{"module":{"running":0,"starts":0,"stops":0}

I updated the module reload code to increment and set the metrics when changes are applied.

CHANGELOG.next.asciidoc

@@ -128,6 +128,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - The `monitoring.elasticsearch.api_key` value is correctly base64-encoded before being sent to the monitoring Elasticsearch cluster. {issue}18939[18939] {pull}18945[18945]
 - Fix kafka topic setting not allowing upper case characters. {pull}18854[18854] {issue}18640[18640]
 - Fix redis key setting not allowing upper case characters. {pull}18854[18854] {issue}18640[18640]
+- Fix config reload metrics (`libbeat.config.module.start/stops/running`). {pull}19168[19168]
 
 *Auditbeat*
 

libbeat/cfgfile/list.go

@@ -84,6 +84,7 @@ func (r *RunnerList) Reload(configs []*reload.ConfigWithMeta) error {
 		r.logger.Debugf("Stopping runner: %s", runner)
 		delete(r.runners, hash)
 		go runner.Stop()
+		moduleStops.Add(1)
 	}
 
 	// Start new runners
@@ -101,8 +102,11 @@ func (r *RunnerList) Reload(configs []*reload.ConfigWithMeta) error {
 		r.logger.Debugf("Starting runner: %s", runner)
 		r.runners[hash] = runner
 		runner.Start()
+		moduleStarts.Add(1)
 	}
 
+	moduleRunning.Set(int64(len(r.runners)))
+
 	return errs.Err()
 }