feat(AppConfig): iterate how apps are managed

- auth clients are always shared, cannot be disabled
- custom connections are enabled by default, can be disabled
- any existing connections can be reconnected regardless of its AppConfig or AppAuthClient states

packages/backend/test/mocks/rest/api/v1/apps/get-config.js

@@ -2,10 +2,8 @@ const getAppConfigMock = (appConfig) => {
   return {
     data: {
       key: appConfig.key,
-      customConnectionAllowed: appConfig.customConnectionAllowed,
-      shared: appConfig.shared,
+      useOnlyPredefinedAuthClients: appConfig.useOnlyPredefinedAuthClients,
       disabled: appConfig.disabled,
-      connectionAllowed: appConfig.connectionAllowed,
       createdAt: appConfig.createdAt.getTime(),
       updatedAt: appConfig.updatedAt.getTime(),
     },