Import JSON files with nested fields

[gabriel-r]

The new JSON import works well for "flat" JSON files. Even very large files seems are parsed nicely and fast. However, the import will only convert the root level elements, while nested fields are imported as text.

Add support for nested JSON fields to support the any generic JSON documents exports.

For example, this JSON content:

[
  {
    "documentation": "For region ap-south-1",
    "expect": {
      "endpoint": {
        "url": "https://appstream2-fips.ap-south-1.api.aws"
      }
    },
    "params": {
      "UseDualStack": true,
      "UseFIPS": true,
      "Region": "ap-south-1"
    }
  },
  {
    "documentation": "For region ap-south-2",
    "expect": {
      "endpoint": {
        "url": "https://appstream2-fips.ap-south-1.amazonaws.com"
      }
    },
    "params": {
      "UseDualStack": false,
      "UseFIPS": true,
      "Region": "ap-south-1"
    }
  }
]

Should result in column names like:

"documentation","expect.endpoint.url","params.UseDualStack","params.UseFIPS","params.Region"
"For region ap-south-1","https://appstream2-fips.ap-south-1.api.aws",true,true,"ap-south-1"
"For region ap-south-2","https://appstream2-fips.ap-south-1.amazonaws.com",false,true,"ap-south-1"

Originally posted by @gabriel-r in https://github.com/hankinsoft/SQLPro/issues/924#issuecomment-1671054289