MM-22786 enterprise metrics for logging (#15313)

Adds metrics for logging engine which are collected by Prometheus.
- current queue level(s)
- rate of logging records emitted
- rate of logging errors

einterfaces/metrics.go

@@ -3,6 +3,8 @@
 
 package einterfaces
 
+import "github.com/mattermost/logr"
+
 type MetricsInterface interface {
 	StartServer()
 	StopServer()
@@ -56,4 +58,6 @@ type MetricsInterface interface {
 	ObservePluginMultiHookIterationDuration(pluginID string, elapsed float64)
 	ObservePluginMultiHookDuration(elapsed float64)
 	ObservePluginApiDuration(pluginID, apiName string, success bool, elapsed float64)
+
+	GetLoggerMetricsCollector() logr.MetricsCollector
 }

einterfaces/mocks/MetricsInterface.go

@@ -4,7 +4,10 @@
 
 package mocks
 
-import mock "github.com/stretchr/testify/mock"
+import (
+	logr "github.com/mattermost/logr"
+	mock "github.com/stretchr/testify/mock"
+)
 
 // MetricsInterface is an autogenerated mock type for the MetricsInterface type
 type MetricsInterface struct {
@@ -31,6 +34,22 @@ func (_m *MetricsInterface) DecrementWebSocketBroadcastUsersRegistered(hub strin
 	_m.Called(hub, amount)
 }
 
+// GetLoggerMetricsCollector provides a mock function with given fields:
+func (_m *MetricsInterface) GetLoggerMetricsCollector() logr.MetricsCollector {
+	ret := _m.Called()
+
+	var r0 logr.MetricsCollector
+	if rf, ok := ret.Get(0).(func() logr.MetricsCollector); ok {
+		r0 = rf()
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).(logr.MetricsCollector)
+		}
+	}
+
+	return r0
+}
+
 // IncrementChannelIndexCounter provides a mock function with given fields:
 func (_m *MetricsInterface) IncrementChannelIndexCounter() {
 	_m.Called()