fix: cap distinct user-agents per endpoint in GrpcUsageTracker - #26778

  193 files  ±0    193 suites  ±0   2h 45m 14s ⏱️ - 11m 29s
  190 tests ±0    189 ✅ ±0  1 💤 ±0  0 ❌ ±0 
1 056 runs  ±0  1 055 ✅ ±0  1 💤 ±0  0 ❌ ±0 

Results for commit eb695f6. ± Comparison against earlier commit b7a4df6.