Improve error message when duplicate assets are found in manifests during publish to build asset registry job

- [ ] This issue is blocking
- [ ] This issue is causing unreasonable pain

We've had some instances of customers asking what to do when they see errors such as:

```
D:\a\1\s\.packages\microsoft.dotnet.arcade.sdk\5.0.0-beta.20364.3\tools\SdkTasks\PublishBuildAssets.proj(40,5): error : Repeated Asset entry: 'Microsoft.DotNet.XHarness.CLI' - '1.0.0-prerelease.20378.1'
D:\a\1\s\.packages\microsoft.dotnet.arcade.sdk\5.0.0-beta.20364.3\tools\SdkTasks\PublishBuildAssets.proj(40,5): error : Repeated Asset entry: 'Microsoft.DotNet.XHarness.iOS.Shared' - '1.0.0-prerelease.20378.1'
D:\a\1\s\.packages\microsoft.dotnet.arcade.sdk\5.0.0-beta.20364.3\tools\SdkTasks\PublishBuildAssets.proj(40,5): error : Repeated Asset entry: 'Microsoft.DotNet.XHarness.SimulatorInstaller' - '1.0.0-prerelease.20378.1'
D:\a\1\s\.packages\microsoft.dotnet.arcade.sdk\5.0.0-beta.20364.3\tools\SdkTasks\PublishBuildAssets.proj(40,5): error : Repeated Asset entry: 'Microsoft.DotNet.XHarness.TestRunners.Common' - '1.0.0-prerelease.20378.1'
D:\a\1\s\.packages\microsoft.dotnet.arcade.sdk\5.0.0-beta.20364.3\tools\SdkTasks\PublishBuildAssets.proj(40,5): error : Repeated Asset entry: 'Microsoft.DotNet.XHarness.TestRunners.NUnit' - '1.0.0-prerelease.20378.1'
D:\a\1\s\.packages\microsoft.dotnet.arcade.sdk\5.0.0-beta.20364.3\tools\SdkTasks\PublishBuildAssets.proj(40,5): error : Repeated Asset entry: 'Microsoft.DotNet.XHarness.TestRunners.Xunit' - '1.0.0-prerelease.20378.1'
D:\a\1\s\.packages\microsoft.dotnet.arcade.sdk\5.0.0-beta.20364.3\tools\SdkTasks\PublishBuildAssets.proj(40,5): error : InvalidOperationException: Duplicate entries are not allowed for publishing to BAR, as this can cause race conditions and unexpected behavior
```

We should consider adding some self service instructions to fix the error, such as telling them to check their asset manifests for duplicates, and to make sure to only publish a given asset from one leg of their build.