Integrate WeChat Official Account support and update configuration

- Added WeChat Official Account configuration options to .env.example and config.go for OAuth2 integration.
- Updated main.go to initialize WeChat OAuth handler and register routes for handling OAuth requests.
- Enhanced documentation to include references for WeChat Official Account functionality.
- Updated route registration to accommodate the new OAuth handler for improved API structure.

internal/routes/wechat_official_routes.go

@@ -0,0 +1,15 @@
+package routes
+
+import (
+	"github.com/gin-gonic/gin"
+
+	oahandler "wx_service/internal/common/wechat_official/handler"
+)
+
+func registerWeChatOfficialRoutes(api *gin.RouterGroup, oauthHandler *oahandler.OAuthHandler) {
+	// 微信公众号（网页授权 OAuth2）
+	oa := api.Group("/wechat/official")
+	{
+		oa.POST("/oauth/code2user", oauthHandler.CodeToUser)
+	}
+}