repo_management/argparse.py:
Add `ArgParseFactory.json2db()` as an ArgumentParser for the `json2db`
script.
Add `ArgParseFactory.string_to_writable_file_path()` for returning a
Path object, that is guaranteed to be a writable file.

tests/test_argparse.py:
Add tests for
`ArgParseFactory.{json2db,string_to_writable_file_path}()`.