[Feat] Add JSON output to r.describe

[NishantBansal2003]

Add JSON output for easy parsing of r.describe output.

Describe the solution you'd like
Add an option for format, such as format=plain for the current output format and format=json for the JSON output.

A possible JSON layout could be:

[
  {
    "values": "0.996534-8.677654"
  },
  {
    "values": "8.677654-16.358774"
  },
  {
    "values": "16.358774-24.040000"
  }
]

Describe alternatives you've considered
Alternatively(helpful for numerical operations or parsing), the JSON layout could look like this:

[
  {
    "min": "0.996534",
    "max": "8.677654"
  },
  {
    "min": "8.677654",
    "max": "16.358774"
  },
  {
    "min": "16.358774",
    "max": "24.040000"
  }
]