feat(container): prioritize openQA tests over LLM container

[okurz]

Motivation:
Prevent the resource-heavy LLM container from starving latency-sensitive
openQA test execution workloads of CPU, disk I/O, and memory resources.

Design Choices:
Set nice level to 12, lower CPUWeight to 50, and use best-effort class 5
for disk I/O. Add OOMScoreAdjust=500 to keep openQA processes safe.

Benefits:
Guarantees a middle-ground resource share for the LLM container while keeping
the host system stable and openQA test environments responsive under load.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (264d797) to head (6c942ec).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #7553   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          423       423           
  Lines        45319     45382   +63     
=========================================
+ Hits         45319     45382   +63     

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