PMM-13910 Fix hottest collections issue

[igroene]

PMM-13910

SUBMODULES-4450

This pull request updates the MongoDB dashboards and their documentation to improve clarity, accuracy, and consistency in how hot collections and operation rates are displayed. The most important changes include standardizing units to "ops/sec", improving query expressions for stability, making collection names more visible in visualizations, and updating documentation to match the dashboard behavior.

Dashboard Query and Visualization Improvements:

• Standardized units for operations per second to "ops/sec" or "ops/s" across all relevant panels in MongoDB_Cluster_Summary.json, MongoDB_ReplSet_Summary.json, and MongoDB_Collections_Overview.json for clarity and consistency. [1] [2] [3] [4] [5] [6] [7]
• Refined PromQL expressions to use stable rate windows (e.g., rate(...[$__rate_interval])) for more accurate and reliable calculation of top hot collections by read and write, and simplified query logic for better maintainability. [1] [2] [3] [4] [5] [6] [7]
• Changed namePlacement from "auto" to "left" in bar gauge visualizations to ensure collection names are always visible, especially for long names. [1] [2] [3] [4] [5] [6] [7]

Documentation Updates:

• Updated descriptions in the dashboard documentation to clarify that hot collection panels use a stable rate window and improved bar gauge label visibility, reflecting the dashboard changes. [1] [2] [3]
• Minor improvements to documentation for clarity and consistency, such as capitalization and section formatting. [1] [2]

These changes collectively enhance the accuracy of displayed metrics, the usability of the dashboards, and the clarity of the accompanying documentation.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 43.49%. Comparing base (1a66249) to head (e6a41f8).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5277      +/-   ##
==========================================
- Coverage   43.66%   43.49%   -0.18%     
==========================================
  Files         414      544     +130     
  Lines       43058    45397    +2339     
  Branches        0      591     +591     
==========================================
+ Hits        18801    19745     +944     
- Misses      22381    23768    +1387     
- Partials     1876     1884       +8     

Flag	Coverage Δ
admin	34.78% <ø> (ø)
unittests	41.29% <ø> (?)

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