Support building data from a single file

Hey, I'm not sure if this is possible already, but I would like to be able to build data from a single file

Example ... `data/projects.json`

There I would have something like:
```json
[
{
"title": "Blueprint",
"description": "Dashboard for creating Android icon packs",
"icon": "/static/images/projects/android/blueprint.png",
"preview": "/static/images/projects/android/blueprint-preview.png",
"link": "https://github.com/jahirfiquitiva/Blueprint/",
"color": "#4d8af0",
"tag": "android",
"stack": [
"android",
"kotlin",
"material design"
]
},
{
"title": "Frames",
"description": "Dashboard for creating Android wallpapers apps",
"icon": "/static/images/projects/android/frames.png",
"preview": "/static/images/projects/android/frames-preview.png",
"link": "https://github.com/jahirfiquitiva/Frames/",
"color": "#35b4ef",
"tag": "android",
"stack": [
"android",
"kotlin",
"material design"
]
}
]
```

And `contentlayer` would be able to return each item as a document of type project, or something like that