Enhancement: Add JSON support

[kilasuit]

Is your feature request related to a problem? Please describe.
Whilst TOML and YAML are supported it should also be able to use json as this is supported as an option in Hugo sites.

Describe the solution you'd like
Add JSON Support

Describe alternatives you've considered
I could use YAML/TOML but it is often much easier programattically amend JSON based FrontMatter outside of this extension.

Additional context
Add any other context or screenshots about the feature request here.

[estruyf]

Thanks @kilasuit for the suggestion. As most use TOML or YAML, support for JSON was a low priority.

In the lastest beta, you'll be able to set the frontMatter.taxonomy.frontMatterType setting to JSON. Once you've done this, it knows to always parse your front matter as JSON.

Sample used for testing:

---
{
  "title": "Page title",
  "lastmod": "2022-01-16T18:46:47.691Z"
}
---

This is some test content.