`dotnetup` should retry install dl / extract or handle 503 better

Exhibited in CI, 503 represents an unavailable server. I'm glad we get the response code but we should maybe have a retry mechanism here. https://dev.azure.com/dnceng-public/public/_build/results?buildId=1469996&view=logs&jobId=2709a726-7db6-5829-ca7b-958b9d664f9e&j=2709a726-7db6-5829-ca7b-958b9d664f9e&t=cbd5e4d2-ff07-56e0-f071-f4be5ccd6b94

The same is true for extraction.

```
Installing dotnet (runtime) 6.0.36, dotnet (runtime) 7.0.20, dotnet (runtime) 8.0.28, dotnet (runtime) 9.0.17, dotnet (runtime) 10.0.9, dotnet (runtime) 11.0.0-preview.6.26311.113, aspnet (runtime) 11.0.0-preview.6.26311.113 to D:\a\_work\1\s\.dotnet...
⚠ Daily builds are not code-signed. Only the SHA-512 hash is verified.
Downloading dotnet (runtime) 10.0.9 ( 33.1 MB / 35.1 MB): 94%
Downloading dotnet (runtime) 6.0.36 ( 11.0 MB / 31.5 MB): 34%
Downloading dotnet (runtime) 9.0.17 ( 0.0 MB / 34.2 MB): 0%
Downloading dotnet (runtime) 7.0.20 ( 0.0 MB / 0.0 MB): 0%
Installing dotnet (runtime) 11.0.0-preview.6.26311.113: 0%
Downloading aspnet (runtime) 11.0.0-preview.6.26311.113 ( 0.0 MB / 45.3 MB): 0%
Installing aspnet (runtime) 11.0.0-preview.6.26311.113: 81%
Installed at D:\a\_work\1\s\.dotnet:
dotnet (runtime) 8.0.28
dotnet (runtime) 10.0.9
dotnet (runtime) 6.0.36
dotnet (runtime) 11.0.0-preview.6.26311.113
dotnet (runtime) 9.0.17
aspnet (runtime) 11.0.0-preview.6.26311.113
The following installs failed:
dotnet (runtime) 7.0.20: Failed to fetch release manifest: Response status code does not indicate success: 503 (Service Unavailable).
Error: Failed to fetch release manifest: Response status code does not indicate success: 503 (Service Unavailable).
Failed to install shared frameworks (6.0, 7.0, 8.0, 9.0, 10.0, 11.0.0-preview.6.26311.113, aspnetcore@11.0.0-preview.6.26311.113) to 'D:\a\_work\1\s\.dotnet' using dotnetup (exit code '1'); falling back to dotnet install script.
```

Start by reproducing the linked CI failure and tracing the dotnetup installation flow for release-manifest downloads and extraction. Check how HTTP 503 responses and extraction failures are currently reported; done means transient failures are retried or handled clearly so the affected runtime installation can complete.

Written by the indexing model from the issue text.