feat: add manual_keep and manual_drop endpoints for parametric test

[genesor]

Description

New endpoints used to validate this new system test: DataDog/system-tests#5617

Motivation

Additional Notes

[pr-commenter]

Benchmarks

Benchmark execution time: 2026-01-05 18:30:24

Comparing candidate commit 390f925 in PR branch ben.db/manual-sampling-system-test with baseline commit 139191e in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 1 metrics, 0 unstable metrics.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.83%. Comparing base (139191e) to head (390f925).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #271      +/-   ##
==========================================
+ Coverage   87.82%   87.83%   +0.01%     
==========================================
  Files          84       84              
  Lines        5659     5664       +5     
==========================================
+ Hits         4970     4975       +5     
  Misses        689      689              

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[datadog-official]

🎯 Code Coverage
• Patch Coverage: 100.00%
• Overall Coverage: 87.84% (+0.01%)

View detailed report

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