Add user to clab_admins group

[kaelemc]

Add the user to the clab_admins group for sudoless clab operation as per v0.64.

Also a new var CLAB_ADMINS. Similar to the SETUP_SSHD, it will default to true. If it is not true, then user won't be added to clab_admins.

PR is in draft state while I test a few things.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 52.45%. Comparing base (f861ff6) to head (66fdd83).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2452      +/-   ##
==========================================
- Coverage   52.48%   52.45%   -0.04%     
==========================================
  Files         172      172              
  Lines       17614    17614              
==========================================
- Hits         9245     9239       -6     
- Misses       7398     7404       +6     
  Partials      971      971              

see 1 file with indirect coverage changes