Add: Local user inventory module

The local user inventory module parses and reports local user
information as discovered in /etc/passwd and /etc/shadow. Additional
bundles are provided to augment the Mission Portal Inventory UI with
interesting information such as all local users, users with locked
accounts, and users that have emtpy passwords.

All local user information is collected for reporting. Additionaly
inventory item for users last password change data is availbale, but
disabled by default until we get epoch time formatting in Mission Portal.

Ref: https://dev.cfengine.com/issues/6213