T5145: Add maximum number of all logins on system

[sever-sever]

Change Summary

maxsyslogins
    maximum number of all logins on system; user is not
    allowed to log-in if total number of all user logins is
    greater than specified number (this limit does not apply
    to user with uid=0)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://vyos.dev/T5145

Component(s) name

login

Proposed changes

How to test

set system login max-login-session '1'
set system login timeout '600'

Try to connect via ssh from a new terminal.
Expected There were too many logins for 'vyos'.

$ ssh vyos@192.168.122.14
Warning: Permanently added '192.168.122.14' (ECDSA) to the list of known hosts.
Welcome to VyOS!

Check out project news at https://blog.vyos.io
and feel free to report bugs at https://vyos.dev

You can change this banner using "set system login banner post-login" command.

VyOS is a free software distribution that includes multiple components,
you can check individual component licenses under /usr/share/doc/*/copyright
There were too many logins for 'vyos'.
Last login: Tue Apr  4 17:08:10 2023 from 192.168.122.1
Connection to 192.168.122.14 closed.

Smoketest:

vyos@r14:~$ /usr/libexec/vyos/tests/smoke/cli/test_system_login.py
/usr/libexec/vyos/tests/smoke/cli/test_system_login.py:23: DeprecationWarning: The distutils package is deprecated and slated for removal in Python 3.12. Use setuptools or check PEP 632 for potential alternatives
  from distutils.version import LooseVersion
test_add_linux_system_user (__main__.TestSystemLogin.test_add_linux_system_user) ... ok
test_radius_kernel_features (__main__.TestSystemLogin.test_radius_kernel_features) ... ok
test_system_login_max_login_session (__main__.TestSystemLogin.test_system_login_max_login_session) ... ok
test_system_login_otp (__main__.TestSystemLogin.test_system_login_otp) ... ok
test_system_login_radius_ipv4 (__main__.TestSystemLogin.test_system_login_radius_ipv4) ... ok
test_system_login_radius_ipv6 (__main__.TestSystemLogin.test_system_login_radius_ipv6) ... ok
test_system_login_user (__main__.TestSystemLogin.test_system_login_user) ... ok
test_system_user_ssh_key (__main__.TestSystemLogin.test_system_user_ssh_key) ... ok

----------------------------------------------------------------------
Ran 8 tests in 28.998s

OK
vyos@r14:~$

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly