move from directory per user, into single json file for export/import

[nemerna]

currently, when exporting, the final export handles each user in a separate directory as follows

example-export
├── kcm
│   ├── USER.json
│   └── group_paths.csv
├── userx
│   ├── USER.json
│   └── group_paths.csv
└── usery
    ├── USER.json
    └── group_paths.csv

change the approach in order to support combining the exported content into a single Json file

then change the import process to expect a single Json file

[nemerna]

@ilan-pinto please take a look to the coresponding branch for this issue
It looks like we can fully support a single Json File for import/export