fix: add aggregatedCount to stackedArea value calc

[pilat-martin]

Frontend Pull Request Description

Fixes CPUMultiLoad metric chart with >= 10 CPUs in Performance Analysis.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have updated change log
• I have been following Definition of done
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new lint warnings
• New and existing unit tests pass locally and on CI with my changes
• Any dependent changes have been merged and published in downstream modules

Screenshots (if applicable)

TBD

Additional Context (if necessary)

TBD

[pavlo-poimanov]

possible regression should be analyzed