PMM-14193 - Enhance MySQL down alert expression

[theTibi]

Updated the expression to better identify down or silent services using service_id, incorporating persistent mapping for service_name and node_name. This change improves the accuracy of alerting for MySQL service availability.

PMM-14193

Link to the Feature Build: SUBMODULES-0

If this PR adds, removes or alters one or more API endpoints, please review and add or update the relevant API documentation as well:

• API Docs updated

If this PR is related to some other PRs in this or other repositories, please provide links to those PRs:

• Links to related pull requests (optional).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 45.78%. Comparing base (14103d8) to head (dfeada0).

Additional details and impacted files

@@            Coverage Diff             @@
##               v3    #4732      +/-   ##
==========================================
- Coverage   45.79%   45.78%   -0.01%     
==========================================
  Files         364      364              
  Lines       37713    37712       -1     
==========================================
- Hits        17272    17268       -4     
- Misses      18785    18787       +2     
- Partials     1656     1657       +1     

Flag	Coverage Δ
managed	46.27% <ø> (-0.01%)	⬇️

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.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.