Add tsa config file to enable validation pipeline

[marcpopMSFT]

Context

MSBuild had been added to the code validation pipeline but was missing the tsa config file. Per the instructions here and after talking to Matt, adding this file

Changes Made

Added a tsa config file by copying from SDK

Testing

Not sure how to test this. I pushed an internal build but the checks didn't run as I'm told they run nightly in a separate pipeline.

Notes

Validation pipeline: https://dev.azure.com/dnceng/internal/_build/results?buildId=2157183&view=results

[JanKrivanek]

Looks good - in case you are sure with having TsaPublish and not TsaOnboard.

The linked arcade help points to runtime sdl-tsa-vars.config that has both. I could only find some description burried in the arcade history https://github.com/dotnet/arcade/blob/ece8fe4f40e0eb788d0ae82472281002f064812a/eng/common/sdl/execute-all-sdl-tools.ps1#L17 - which seems to suggest TsaPublish should be set to onboard, and TsaPublish should be only used after that. But hopefully this confusing statefulness is already not applicable

[marcpopMSFT]

@JanKrivanek it's not clear to me if that flag is required or not. I checked and nearly every other repo does set that flag to true (except for sdk and installer) so I went ahead and added it. I double checked with Matt and he suggested adding it as well. This PR is ready to go in whenever.

[JanKrivanek]

Thanks @marcpopMSFT!

It would be nice if arcade had that param documented (since they refer to that in sample config). Thanks for making extra effort to attempt to extract some info and convention.

This is good to go.