Add Ivanti Connect Secure OSPlugin

[skepppy]

Initial version for an OSPlugin that works for some of the versions of Ivanti Connect Secure, a VPN product.

Later, I would like to add some target-query plugins that parse certain log files that are available.

To the reviewer: Among other things, I don't really know when it is good to raise an exception versus printing an error message + return.

[codecov]

Codecov Report

❌ Patch coverage is 50.74627% with 99 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.50%. Comparing base (c9b1e1d) to head (bd4a9ee).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
dissect/target/plugins/os/unix/linux/iveos/_os.py	50.74%	99 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1600      +/-   ##
==========================================
- Coverage   81.10%   80.50%   -0.60%     
==========================================
  Files         401      402       +1     
  Lines       35017    35222     +205     
==========================================
- Hits        28399    28355      -44     
- Misses       6618     6867     +249     

Flag	Coverage Δ
unittests	80.50% <50.74%> (-0.60%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[codspeed-hq]

Merging this PR will not alter performance

✅ 12 untouched benchmarks

---

_{Comparing skepppy:add/ivanti-connect-secure (bd4a9ee) with main (0f31fe5)}