MM-39215: Add DBStatsCollector to metrics (#21957)

https://mattermost.atlassian.net/browse/MM-39215

```release-note
We now have Grafana metrics for DB connection metrics.
They are:
max_open_connections
open_connections
in_use_connections
idle_connections
wait_count_total
wait_duration_seconds_total
max_idle_closed_total
max_idle_time_closed_total
max_lifetime_closed_total
```

app/platform/service_test.go

@@ -141,6 +141,7 @@ func TestMetrics(t *testing.T) {
 		mockMetricsImpl := &mocks.MetricsInterface{}
 		mockMetricsImpl.On("Register").Return()
 		mockMetricsImpl.On("ObserveStoreMethodDuration", mock.Anything, mock.Anything, mock.Anything).Return()
+		mockMetricsImpl.On("RegisterDBCollector", mock.AnythingOfType("*sql.DB"), "master")
 
 		th := Setup(t, StartMetrics(), func(ps *PlatformService) error {
 			ps.metricsIFace = mockMetricsImpl

einterfaces/metrics.go

@@ -4,12 +4,15 @@
 package einterfaces
 
 import (
+	"database/sql"
+
 	"github.com/mattermost/mattermost-server/v6/model"
 	"github.com/mattermost/mattermost-server/v6/shared/mlog"
 )
 
 type MetricsInterface interface {
 	Register()
+	RegisterDBCollector(db *sql.DB, name string)
 
 	IncrementPostCreate()
 	IncrementWebhookPost()

einterfaces/mocks/MetricsInterface.go

@@ -9,6 +9,8 @@ import (
 	mock "github.com/stretchr/testify/mock"
 
 	model "github.com/mattermost/mattermost-server/v6/model"
+
+	sql "database/sql"
 )
 
 // MetricsInterface is an autogenerated mock type for the MetricsInterface type
@@ -302,6 +304,11 @@ func (_m *MetricsInterface) Register() {
 	_m.Called()
 }
 
+// RegisterDBCollector provides a mock function with given fields: db, name
+func (_m *MetricsInterface) RegisterDBCollector(db *sql.DB, name string) {
+	_m.Called(db, name)
+}
+
 // SetReplicaLagAbsolute provides a mock function with given fields: node, value
 func (_m *MetricsInterface) SetReplicaLagAbsolute(node string, value float64) {
 	_m.Called(node, value)

store/sqlstore/store.go

@@ -301,6 +301,9 @@ func (ss *SqlStore) initConnection() {
 	if ss.DriverName() == model.DatabaseDriverMysql {
 		ss.masterX.MapperFunc(noOpMapper)
 	}
+	if ss.metrics != nil {
+		ss.metrics.RegisterDBCollector(ss.masterX.DB.DB, "master")
+	}
 
 	if len(ss.settings.DataSourceReplicas) > 0 {
 		ss.ReplicaXs = make([]*sqlxDBWrapper, len(ss.settings.DataSourceReplicas))
@@ -312,6 +315,9 @@ func (ss *SqlStore) initConnection() {
 			if ss.DriverName() == model.DatabaseDriverMysql {
 				ss.ReplicaXs[i].MapperFunc(noOpMapper)
 			}
+			if ss.metrics != nil {
+				ss.metrics.RegisterDBCollector(ss.ReplicaXs[i].DB.DB, "replica-"+strconv.Itoa(i))
+			}
 		}
 	}
 
@@ -325,6 +331,9 @@ func (ss *SqlStore) initConnection() {
 			if ss.DriverName() == model.DatabaseDriverMysql {
 				ss.searchReplicaXs[i].MapperFunc(noOpMapper)
 			}
+			if ss.metrics != nil {
+				ss.metrics.RegisterDBCollector(ss.searchReplicaXs[i].DB.DB, "searchreplica-"+strconv.Itoa(i))
+			}
 		}
 	}
 

store/sqlstore/store_test.go

@@ -24,6 +24,7 @@ import (
 	"github.com/mattermost/mattermost-server/v6/db"
 	"github.com/mattermost/mattermost-server/v6/einterfaces/mocks"
 	"github.com/mattermost/mattermost-server/v6/model"
+	"github.com/mattermost/mattermost-server/v6/plugin/plugintest/mock"
 	"github.com/mattermost/mattermost-server/v6/store"
 	"github.com/mattermost/mattermost-server/v6/store/searchtest"
 	"github.com/mattermost/mattermost-server/v6/store/storetest"
@@ -731,6 +732,7 @@ func TestReplicaLagQuery(t *testing.T) {
 		defer mockMetrics.AssertExpectations(t)
 		mockMetrics.On("SetReplicaLagAbsolute", tableName, float64(1))
 		mockMetrics.On("SetReplicaLagTime", tableName, float64(1))
+		mockMetrics.On("RegisterDBCollector", mock.AnythingOfType("*sql.DB"), "master")
 
 		store := &SqlStore{
 			rrCounter: 0,