feat: customize load in agent or in app

Author: chenzheqi

agent.js

@@ -1,5 +1,7 @@
 'use strict';
 
 module.exports = agent => {
-  require('./lib/loader')(agent);
+  if (agent.config.sequelize.agent) {
+    require('./lib/loader')(agent);
+  }
 };

app.js

@@ -1,6 +1,7 @@
 'use strict';
 
 module.exports = app => {
-  require('./lib/loader')(app);
+  if (app.config.sequelize.app) {
+    require('./lib/loader')(app);
+  }
 };
-

config/config.default.js

@@ -1,6 +1,8 @@
 'use strict';
 
 exports.sequelize = {
+  agent: false,
+  app: true,
   dialect: 'mysql',
   database: '',
   host: 'localhost',