Add support for OpenCover

[uhafner]

Followup for jenkinsci/coverage-model#64

Add support for the coverage format OpenCover.

Fixes jenkinsci/code-coverage-api-plugin#770.

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (c847de6) 77.32% compared to head (9025ce1) 77.30%.
Report is 4 commits behind head on main.

Files	Patch %	Lines
...s/plugins/coverage/metrics/steps/CoverageTool.java	50.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main      #60      +/-   ##
============================================
- Coverage     77.32%   77.30%   -0.03%     
  Complexity      742      742              
============================================
  Files            47       47              
  Lines          2633     2635       +2     
  Branches        252      252              
============================================
+ Hits           2036     2037       +1     
- Misses          514      515       +1     
  Partials         83       83              

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[jonesbusy]

All good from me, thank you!