[Security] Add 2-day minimum release age cooldown (incident-51987)

[SeanMeyer]

Summary

• Adds npmMinimalAgeGate: "2d" to .yarnrc.yml to configure Yarn Berry to refuse packages published less than 2 days ago during lockfile generation
• Part of security campaign (incident-51987) to add supply chain attack cooldowns across DataDog repositories
• Requires Yarn Berry >= 4.10.0 (this repo uses 4.10.3)

Test plan

• Verify yarn install still works with the new setting
• Confirm no lockfile changes are introduced by this config-only change

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.69%. Comparing base (3f2947a) to head (a864eed).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #685   +/-   ##
=======================================
  Coverage   77.69%   77.69%           
=======================================
  Files          12       12           
  Lines        1112     1112           
  Branches      350      350           
=======================================
  Hits          864      864           
  Misses        118      118           
  Partials      130      130           

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