[Perf] Add PerfTestBase and BatchPerfTest

[annatisch]

Fixes #20816
Fixes #21384
Fixes #21159

[mikeharder]

I didn't review the code line-by-line, but the APIs look correct.

I recommend adding a sample test that extends BatchPerfTest, something like https://github.com/Azure/azure-sdk-for-net/pull/24653/files#diff-5ebbae98f50d4148984513195f10702a48ae2b56dfbfaa9220b591c88b710978.

I also recommend running a few real-world tests like blop upload/download/list-blobs to verify no change in results.

[annatisch]

Thanks @mikeharder - I added that sample to the documentation, and ran the blob storage tests (with and without proxy)

[mikeharder]

Thanks @mikeharder - I added that sample to the documentation, and ran the blob storage tests (with and without proxy)

How do you feel about adding the sample MessageReceiveTest to the system_perfstress folder, so it can be easily run without needing to copy/paste from the docs?

[annatisch]

Sure thing. Added.