Clarify dotnet new NuGet source option

[Copilot]

The --add-source|--nuget-source docs implied the option adds a source to the configured NuGet source list. The option only adds a source for the current dotnet new operation.

• Clarified source behavior

  • Updated dotnet new install, dotnet new update, and dotnet new details to state that --nuget-source is used in addition to configured sources for the command only.
  • Explicitly notes that the option doesn't modify NuGet configuration.

• Cleaned related command docs

  • Corrected the dotnet new update option heading to include --nuget-source.
  • Fixed copied wording that referenced dotnet new install from the dotnet new update page.

• Fixes The --nuget-source option description could be misleading #55188

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Internal previews

File	Preview link
docs/core/tools/dotnet-new-details.md	Preview published page
docs/core/tools/dotnet-new-install.md	Preview published page
docs/core/tools/dotnet-new-update.md	Preview published page

[Copilot]

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[adegeo]

@copilot I think the "in addition to" clause clears up the ambiguity. Remove the for this command only. The option doesn't add the source to your NuGet configuration clause as it doesn't add value.

[Copilot]

@copilot I think the "in addition to" clause clears up the ambiguity. Remove the for this command only. The option doesn't add the source to your NuGet configuration clause as it doesn't add value.

Addressed in 78ecf3a.