Improve resource.Quantity to float conversion for SLOs (#1308)

[levan-m]

What does this PR do?

Cherry-pick #1308

Motivation

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Additional Notes

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Minimum Agent Versions

Are there minimum versions of the Datadog Agent and/or Cluster Agent required?

• Agent: vX.Y.Z
• Cluster Agent: vX.Y.Z

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Checklist

• PR has at least one valid label: bug, enhancement, refactoring, documentation, tooling, and/or dependencies
• PR has a milestone or the qa/skip-qa label

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 55.21%. Comparing base (7b3a6ed) to head (3c44b31).

Additional details and impacted files

@@           Coverage Diff           @@
##             v1.8    #1322   +/-   ##
=======================================
  Coverage   55.20%   55.21%           
=======================================
  Files         247      247           
  Lines       28383    28384    +1     
=======================================
+ Hits        15670    15671    +1     
  Misses      11827    11827           
  Partials      886      886           

Flag	Coverage Δ
unittests	55.21% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
controllers/datadogslo/slo.go	61.38% <100.00%> (+0.38%)	⬆️

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