Add `dotnet nuget push --skip-duplicates` synonym for `--skip-duplicate`

[Smaug123]

NuGet Product(s) Involved

NuGet.exe, dotnet.exe

The Elevator Pitch

Add a synonym --skip-duplicates for --skip-duplicate.

Additional Context and Details

For at least two reasons, there is a strong basin of attraction leading users to --skip-duplicates rather than the (correct) --skip-duplicate:

• "Skip duplicate" is ungrammatical; "skip duplicates" is grammatically correct.
• dotnet nuget push is capable of pushing multiple packages in the same invocation.

In fact over the past year or so I have incorrectly spelled the argument --skip-duplicates twice (to the best of my recollection).

This issue is dotnet/sdk#41289 .