The file extensions used in `cli_load.py` has '.' prefix. The comparison
in `get_filenames_in_dir` uses the strings from
`ext = file_path.suffix.lstrip(".")` resulting in strings without '.'
prefix. We fix this by giving extensions without '.' prefix in the
default list of extensions to compare against.
The file_path generated are of type PosixPath, where as string list is
expected. We fix this by converting PosixPath to string before
constructing the list.
