Add retry to VSWhere.exe download / consider sourcing from owned storage

[MattGal]

We download VSWhere here: https://github.com/dotnet/arcade/blob/master/eng/common/tools.ps1#L349

Which fails in some builds with:
##[error](NETCORE_ENGINEERING_TELEMETRY=InitializeToolset) The remote name could not be resolved: 'github-production-release-asset-2e65be.s3.amazonaws.com'

We should definitely:

• Add retry logic to tools.ps1 for any download (a simple retry wrapper should do, with say 5 total retries and 30 sec pauses

And optionally:

• Check for existence of VSWhere on the machine already (which would be found on the machine used in this build failure : https://dev.azure.com/dnceng/public/_build/results?buildId=397311 )
• Store VSWhere on NetCoreNativeAssets or other storage account (though this still can fail just like AWS storage can)

[MattGal]

Looks like this already happened (https://github.com/dotnet/arcade/blob/main/eng/common/tools.ps1#L516) so closing this.