feat(content): handle json arrays

[benjamincanac]

This PR will allow to create .json files with arrays at the root:

[
  {
    "name": "Sébastien Chopin",
    "slug": "atinux"
  },
  {
    "name": "Krutie Patel",
    "slug": "krutiepatel"
  },
  {
    "name": "Sergey Bedritsky",
    "slug": "sergeybedritsky"
  }
]

will insert:

[
  {
    "name": "Sébastien Chopin",
    "slug": "atinux",
    "dir": "/authors",
    "path": "/authors/atinux",
    "extension": ".json"
  },
  {
    "name": "Krutie Patel",
    "slug": "krutiepatel",
    "dir": "/authors",
    "path": "/authors/krutiepatel",
    "extension": ".json"
  },
  {
    "name": "Sergey Bedritsky",
    "slug": "sergeybedritsky",
    "dir": "/authors",
    "path": "/authors/sergeybedritsky",
    "extension": ".json"
  }
]

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Description

This PR allows slug override.

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes (if not applicable, please state why)

[stronglify13]

This feature is lost in Nuxt Content 2 ??
or if could someone help me, how should I implement it?