Initial Cisco FTDv support

[dteslya]

This PR follows hellt/vrnetlab#154 and adds Cisco FTDv support. I've included an example lab topology I used for testing and some basic documentation.

[codecov]

Codecov Report

Merging #1783 (747e40f) into main (40084e3) will decrease coverage by 0.18%.
Report is 2 commits behind head on main.
The diff coverage is 4.87%.

❗ Current head 747e40f differs from pull request most recent head 4774684. Consider uploading reports for the commit 4774684 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1783      +/-   ##
==========================================
- Coverage   51.45%   51.27%   -0.18%     
==========================================
  Files         145      146       +1     
  Lines       14132    14173      +41     
==========================================
- Hits         7271     7267       -4     
- Misses       6044     6086      +42     
- Partials      817      820       +3     

Files	Coverage Δ
clab/register.go	100.00% <100.00%> (ø)
cmd/generate.go	65.47% <ø> (ø)
nodes/vr_ftdv/vr-ftdv.go	2.50% <2.50%> (ø)

... and 1 file with indirect coverage changes