refactor(config): rename package _config to config with cfg alias

The config package used `package _config` with a leading underscore,
which is unconventional in Go. Rename to `package config` (matching the
directory name) and use `cfg` as the standard import alias across all
93 importing files.

server/api/api_server.go

@@ -2,7 +2,7 @@ package api
 
 import (
 	"context"
-	_config "erupe-ce/config"
+	cfg "erupe-ce/config"
 	"fmt"
 	"net/http"
 	"os"
@@ -19,14 +19,14 @@ import (
 type Config struct {
 	Logger      *zap.Logger
 	DB          *sqlx.DB
-	ErupeConfig *_config.Config
+	ErupeConfig *cfg.Config
 }
 
 // APIServer is Erupes Standard API interface
 type APIServer struct {
 	sync.Mutex
 	logger         *zap.Logger
-	erupeConfig    *_config.Config
+	erupeConfig    *cfg.Config
 	db             *sqlx.DB
 	httpServer     *http.Server
 	isShuttingDown bool