Bug: The plugin 'redirect' cannot be enabled when editing route

[fukiki]

Bug report

Describe the bug

The plugin 'redirect' cannot be enabled in step 3 'Plugin Config' when editing route.

How to Reproduce

1. Go to 'Route'
2. Select one route, click on 'Edit', go to step 3 'Plugin Config'
3. Select plugin 'redirect', enable plugin and add config.
   
4. Submit and update route successfully.
5. Click on 'Edit' to check the route plugins, and plugin 'redirect' is disabled.
   Actually, there is no plugin 'redirect' params when sending the request.
   

Expected behavior

The plugin 'redirect' can be enabled in step 3 'Plugin Config' when editing route.

There are two ways to fix this issue：

1. The plugin 'redirect' param should be add in step 3 'Plugin Config' when editing route.
2. When editing the route, plugin 'redirect' can not be displayed in step 3.

Actually, the plugin 'redirect' could been configured in step 1 when edit route, and I prefer the way 2.

System information

• OS: macOS, centos
• Browser：Chrome
• Version: master branch