Add Azure perf testing to load testing

[Rick-Anderson]

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Document Details

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• ID: ce92350f-25e5-63bc-c815-a8a41b2253c3
• Version Independent ID: e8f9ec21-4e0a-054e-b9ba-fd27e71e31a0
• Content: ASP.NET Core load/stress testing
• Content Source: aspnetcore/test/load-tests.md
• Product: aspnet-core
• Technology: aspnetcore-test
• GitHub Login: @Jeremy-Meng
• Microsoft Alias: riande