enum_psk: Cleanup

[bcoles]

Prior to this PR, the module used unintuitive method names, unnecessarily passed and returned complex objects to/from methods, passed variables to methods for no reason other than to return the variables later, and wrapped the entire run method in a is_root? and tbl.rows.empty? conditionals. This has been cleaned up.

Also:

• Adds documentation
• Adds notes
• Resolves Rubocop violations
• Replaces /bin/ls -1 #{dir} with dir method from Post library
• Removes a useless TODO

There is a lot of room for improvement in this module. Ideally the module would be expanded to also capture other NetworkManager configuration information (including credentials, such as 802.1x creds). This is out of scope for this PR.

---

I used a dumb test file to test this:

# cat /etc/NetworkManager/system-connections/test 
asdf
psk=1234567890
asdf=asdf

[adfoster-r7]

Worked for me with a dummy file from https://lauri.xn--vsandi-pxa.com/cfgmgmt/network-manager-system-connections.html - it even picked up the .swp file as an edge case, which wasn't intentional on my part

msf6 post(linux/gather/enum_psk) > run session=-1

[*] Reading file /etc/NetworkManager/system-connections//Wired connection 1
[*] Reading file /etc/NetworkManager/system-connections//.Wired connection 1.swp

802-11-wireless-security
========================

 AccessPoint-Name    PSK
 ----------------    ---
 Wired connection 1  salakala

Database creds stored correctly:

msf6 post(linux/gather/enum_psk) > creds
Credentials
===========

host  origin           service  public              private   realm  private_type  JtR Format
----  ------           -------  ------              -------   -----  ------------  ----------
      192.168.123.128           Wired connection 1  salakala         Password  

[adfoster-r7]

Release Notes

Improves the linux/gather/enum_psk module, and adds documentation