Add parser for /etc/group files

[chb2mn]

Description of problem:

I'd like Plaso to be able to parse a group file like that found on linux or mac systems

Command line and arguments:

`psteal.py --parsers "!filestat"

Source data:

group.zip

Plaso version:

plaso - psteal version 20220930

Operating system Plaso is running on:

Kubuntu22