Add Linux VM kind

[jmussmann]

This PR add support for a vrnlab linux VM kind.

The corresponding PR in the vrnetlab repository is "Add Ubuntu Support #183" for ubuntu.

The code would also support other linux distribution. This is why the kind is called vr_linux and not vr_ubuntu.

[hellt]

I plan to review/merge this in the coming days

[codecov]

Codecov Report

Attention: Patch coverage is 6.25000% with 30 lines in your changes missing coverage. Please review.

Project coverage is 53.72%. Comparing base (9ecdf0e) to head (602d660).
Report is 51 commits behind head on main.

❗ Current head 602d660 differs from pull request most recent head 336eec1

Please upload reports for the commit 336eec1 to get more accurate results.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1976      +/-   ##
==========================================
+ Coverage   53.58%   53.72%   +0.13%     
==========================================
  Files         160      163       +3     
  Lines       11536    11631      +95     
==========================================
+ Hits         6182     6249      +67     
- Misses       4489     4507      +18     
- Partials      865      875      +10     

Files	Coverage Δ
clab/register.go	100.00% <100.00%> (ø)
nodes/generic_vm/generic_vm.go	3.22% <3.22%> (ø)

... and 22 files with indirect coverage changes

[hellt]

thanks @jmussmann !
both this and hellt/vrnetlab#198 have been merged. Appreciate your work on this!