refactor(processor/openstack): Decouple monitor agent config from actor

[gfieni]

This PR refactors the OpenStack pre-processor so the monitor agent configuration is carried by a dedicated dataclass instead of actor constructor parameters.

[codecov]

Codecov Report

❌ Patch coverage is 76.19048% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.08%. Comparing base (a2542cc) to head (f8a91a2).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
.../powerapi/processor/pre/openstack/monitor_agent.py	72.72%	3 Missing ⚠️
src/powerapi/processor/pre/openstack/actor.py	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #835      +/-   ##
==========================================
+ Coverage   72.02%   72.08%   +0.05%     
==========================================
  Files          90       90              
  Lines        3003     3009       +6     
==========================================
+ Hits         2163     2169       +6     
  Misses        840      840              

Files with missing lines	Coverage Δ
src/powerapi/cli/generator.py	89.14% <100.00%> (+0.09%)	⬆️
src/powerapi/processor/pre/openstack/actor.py	66.66% <66.66%> (ø)
.../powerapi/processor/pre/openstack/monitor_agent.py	75.00% <72.72%> (+2.08%)	⬆️

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