[Question] Create tags that don't exist with source-filesystem plugin

Right now, in my `gridsome.config.js` I have the following plugin:

```javascript
{
use: '@gridsome/source-filesystem',
options: {
typeName: 'Post',
path: 'content/posts/**/*.md',
route: '/post/:id',
refs: {
tags: {
typeName: 'Tag',
route: '/tag/:title',
create: true,
},
},
},
},
```

This way, all tag entities will be created automatically. However, I want to add extra metadata to some of the tags using a custom .md file with the metadata and content for that tag, but I still want to have the rest of the tags created automatically. How would I go about this?