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

  168 files  ±0    168 suites  ±0   2h 45m 45s ⏱️ + 29m 21s
  294 tests ±0    293 ✅ ±0  1 💤 ±0  0 ❌ ±0 
1 657 runs  ±0  1 656 ✅ ±0  1 💤 ±0  0 ❌ ±0 

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