Add file system checks for other shadow and passwd/group files

[cmhe]

Is your feature request related to a problem? Please describe.
We currently have os-02 and os-03 which checks the permissions of /etc/shadow and /etc/passwd.

There are other files related to those, which are currently ignored:

• /etc/shadow- (backup for /etc/shadow
• /etc/gshadow (might contain group password hashes)
• /etc/gshadow- (backup for /etc/gshadow)
• /etc/passwd- (backup for /etc/passwd)
• /etc/group (contains available groups and memberships)
• /etc/group- (backup for /etc/group)

Describe the solution you'd like
Add checks for those files as well

[chris-rock]

Great idea @cmhe Happy to accept PRs to improve the controls