fix(db): sets max open and idle connections for postgres

When postgres is used as backing database for headscale, it does not set
a limit on maximum open and idle connections which leads to hundreds of
open connections to the postgres server. This commit fixes that by
setting up a connection pool while creating the gorm DB instance.

hscontrol/db/db.go

@@ -12,13 +12,14 @@ import (
 
 	"github.com/glebarez/sqlite"
 	"github.com/go-gormigrate/gormigrate/v2"
-	"github.com/juanfont/headscale/hscontrol/notifier"
-	"github.com/juanfont/headscale/hscontrol/types"
-	"github.com/juanfont/headscale/hscontrol/util"
 	"github.com/rs/zerolog/log"
 	"gorm.io/driver/postgres"
 	"gorm.io/gorm"
 	"gorm.io/gorm/logger"
+
+	"github.com/juanfont/headscale/hscontrol/notifier"
+	"github.com/juanfont/headscale/hscontrol/types"
+	"github.com/juanfont/headscale/hscontrol/util"
 )
 
 const (
@@ -360,10 +361,17 @@ func openDB(dbType, connectionAddr string, debug bool) (*gorm.DB, error) {
 		return db, err
 
 	case Postgres:
-		return gorm.Open(postgres.Open(connectionAddr), &gorm.Config{
+		db, err := gorm.Open(postgres.Open(connectionAddr), &gorm.Config{
 			DisableForeignKeyConstraintWhenMigrating: true,
 			Logger:                                   dbLogger,
 		})
+
+		sqlDB, _ := db.DB()
+		sqlDB.SetMaxOpenConns(10)
+		sqlDB.SetMaxIdleConns(10)
+		sqlDB.SetConnMaxIdleTime(time.Hour)
+
+		return db, err
 	}
 
 	return nil, fmt.Errorf(