refactor(app-config): rename allow_custom_connection as custom_connection_allowed

packages/backend/src/models/__snapshots__/app-config.test.js.snap

@@ -3,10 +3,6 @@
 exports[`AppConfig model > jsonSchema should have correct validations 1`] = `
 {
   "properties": {
-    "allowCustomConnection": {
-      "default": false,
-      "type": "boolean",
-    },
     "connectionAllowed": {
       "default": false,
       "type": "boolean",
@@ -14,6 +10,10 @@ exports[`AppConfig model > jsonSchema should have correct validations 1`] = `
     "createdAt": {
       "type": "string",
     },
+    "customConnectionAllowed": {
+      "default": false,
+      "type": "boolean",
+    },
     "disabled": {
       "default": false,
       "type": "boolean",
@@ -39,3 +39,5 @@ exports[`AppConfig model > jsonSchema should have correct validations 1`] = `
   "type": "object",
 }
 `;
+
+exports[`AppConfig model > virtualAttributes should return correct properties 1`] = `null`;