[Microsoft.ClientModel.TestFramework] Copy improvements from core test framework, add better integration tests, fix some tooling issues

[m-redding]

This PR makes a number of changes to the unbranded test framework:

• Sets up the test-proxy tool in the tools manifest
• Fixes an issue with the dotnet tool restore call which requires --add-source to work properly. Without it, the tool fails to restore in the pipeline (no locally). My hunch is that this is most likely due to 'Dotnet tool restore' does not work correctly when NUGET_PACKAGES (global-packages) is set to an alternative location  dotnet/sdk#11432 since our pipeline sets NUGET_PACKAGES, and the --add-source bypasses it
• Contributes to Bring improvements over to Microsoft.ClientModel.TestFramework #53190
• Brings over some of the test clients and functional tests from Azure.Core.TestFramework to provide better integration tests
• Removes some lower quality tests

[github-actions]

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Microsoft.ClientModel.TestFramework