Add option for management client passthrough

[jkroepke]

What this PR does / why we need it

Which issue this PR fixes

(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

• fixes Openvpn management interface passthrough (OpnSense compatibility) #146

Special notes for your reviewer

Particularly user-facing changes

Checklist

Complete these before marking the PR as ready to review:

• DCO signed
• The PR title has a summary of the changes
• The PR body has a summary to reflect any significant (and particularly user-facing) changes introduced by this PR

[codecov]

Codecov Report

Attention: 66 lines in your changes are missing coverage. Please review.

Comparison is base (3862426) 73.01% compared to head (0a83ea2) 73.08%.

Files	Patch %	Lines
internal/openvpn/passthrough.go	69.59%	27 Missing and 18 partials ⚠️
internal/openvpn/main.go	68.00%	5 Missing and 3 partials ⚠️
internal/openvpn/handler.go	64.28%	3 Missing and 2 partials ⚠️
pkg/testutils/main.go	90.69%	2 Missing and 2 partials ⚠️
cmd/daemon/root.go	50.00%	2 Missing ⚠️
internal/utils/lookup.go	87.50%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #180      +/-   ##
==========================================
+ Coverage   73.01%   73.08%   +0.07%     
==========================================
  Files          48       49       +1     
  Lines        1890     2129     +239     
==========================================
+ Hits         1380     1556     +176     
- Misses        429      466      +37     
- Partials       81      107      +26     

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